ELEMENTS OF PHYSICAL 
GEOGRAPHY 



ELEMENTS OF PHYSICAL 
GEOGRAPHY 



BY 



THOMAS CRAMER HOPKINS, Ph.D. 



PROFESSOR OF GEOLOGY IN 
SYRACUSE UNIYERSITY 



NEW EDITION 



BENJ. H. SANBORN & CO. 

CHICAGO NEW YORK BOSTON 



Q& 






Copyright, 1908, 
By THOMAS CRAMER HOPKINS 

Copyright, 1919, 
By BENJ. H. SANBORN & CO. 



NOV -6 19/9 



©CI.A535716 



s 



PREFACE TO THE FIRST EDITION 

There are good textbooks on physical geography, but there 
are many teachers and school departments not satisfied with 
any of them. The author has endeavored to meet the require- 
ments of these teachers as far as such needs could be ascertained. 
With a subject as broad as physical geography there will al- 
ways be lack of uniformity in the manner of presentation, as 
well as in the subject matter. The subject is one which is 
undergoing many changes, and it is possible that both the 
teachers and the subject may be ahead of present textbooks 
in many particulars. . . . 

Every class in physical geography should have more or less 
laboratory and field work associated with the textbook. One 
of the functions of the textbook — not the only one, by any 
means — is to serve as a handbook, which the pupil studies 
as an aid in the interpretation of what he sees in the labora- 
tory. . . . 

The text . . . aims to assist both teacher and pupil into the 
spirit of one of the most inspiring subjects in our schools ; to 
bring the pupil into contact with Nature' in such a way that he 
may see and realize his own position in this world of complex 
activities, so that by observing more closely the familiar phe- 
nomena surrounding him in his daily life he may extend his 
observations and knowledge through the less known into the 
unknown, and thus be an intelligent part of the world in which 
he lives. 

The author is indebted to many teachers of physical geography 
in many states in the preparation of this text. After the manu- 
script was written it was submitted to a number of prominent 
teachers in high schools, academies, and colleges for criticism, 



VI PREFACE TO THE FIRST EDITION 

and the valuable suggestions made by them are incorporated 
as far as possible. Especially does he desire to express his 
indebtedness to the following eminent teachers for valuable 
aid : Professor C. E. Peet, Lewis Institute, Chicago ; Miss 
Mary G. Sullivan, Buffalo High School ; Dr. C. H. Richard- 
son, the author's colleague in Syracuse University ; Miss 
Jennie T. Martin, City Schools, Washington, D. C. ; Professor 
James H. Smith, Chicago High School ; Dr. F. H. H. Calhoun, 
Clemson College, S. C. ; Sarah Emerson Green, formerly the 
author's assistant at Syracuse University ; and P. F. Schneider 
of Syracuse. The first three above named read both the manu- 
script and the proof with painstaking care, and the others gave 
valuable aid in reading either the proof or the manuscript. 
Dr. H. A. Peck, Professor of Astronomy, gave many valuable 
suggestions on Chapter I, and Morgan R. Sanford, local fore- 
caster for the U. S. Weather Bureau, did the same in Chap- 
ter X [The Atmosphere]. 

For the photographs illustrating the text the author is deeply 
indebted to many friends and colleagues who are credited else- 
where. Special thanks are due to the U. S. Geological Sur- 
vey, the U. S. Fish Commission, the Maryland and Vermont 
State Geological Surveys, and the American Museum of Natural 
History. Where not otherwise credited the photographs are 
by the author, except a very few where the photographer is 
not known. The illustrations and explanations of the same 
form a very important part of the text and should be studied 
as carefully as the words. In some instances the picture illus- 
trates the text, in others the text is an explanation of a principle 

best learned from the picture. 

T 1 C "FT 

Syracuse University ■*•• °* X1, 

May, 1908 



PREFACE TO THE SECOND EDITION Vll 

PREFACE TO THE SECOND EDITION 

The development that has taken place in physical geography 
and the changes that have taken place in the teaching of the 
subject during the past eleven years, have made a revision of 
this book advisable. The entire text has been rewritten and 
rearranged. The suggestions of teachers in different parts of 
the country have been considered and all such that promised 
to be an improvement have been incorporated in the new 
edition. 

The rearrangement of chapters will commend itself to most 
teachers as an improvement. However, conditions vary, and 
many teachers will have sufficient reasons for taking the chapters 
up in a different order. This they can easily do, since each 
chapter is complete in itself, and cross references abound. 

Many new illustrations have been added and some of the 
old ones have been omitted. I am again indebted to many 
colleagues and other friends for these fine photographs. 

The author wishes to acknowledge here the many kind words 
of commendation from teachers in all parts of the country, and 
hopes that the new edition will prove to be even more helpful 
than the first. It is his belief that the great World War just 
ended will give the subject of geography more prominence in 
the schools than it has had in the past. 

T. C. H. 

Sykacuse, 'N. Y. 
August, 1919 



CONTENTS 











PAGE 
V 










. vii 










ix 


CHAPTEI 
I. 


e 

The Earth as a Planet . 








1 


II. 










35 


III. 


The Ocean 








90 


IV. 


Shore Lines and Coast Features 








126 


V. 


The Land ..... 








170 


VI. 


Mantle Rock and Soil 








203 


VII. 










227 


VIII. 










263 


IX. 










313 


X. 


Lakes and Swamps 








345 


XI. 


Crustal Movement and Vulcanism 








370 


XII. 


Plains and Plateaus . 








391 


XIII. 


Mountains and Minor Topographic Features 




422 


XIV. 


Geography op Plants, Animals, and Man 




453 


Appendix I 




501 






502 






505 


Index 


• • o o • • • 








513 



INTRODUCTION 

We travel more than our grandparents did. We go oftener, 
we go faster, we go farther. We see, or at least we have the 
opportunity of seeing, more of the world than preceding genera- 
tions did. 

Whether the object of travel be business or pleasure and 
education, a scientific knowledge of the earth's features in- 
creases both the profit and the pleasure of traveling. The 
skilled artist sees more in a good painting than does one who is 
ignorant of art. The skilled geographer sees more in a land- 
scape than does one who has not had such training. He is 
able to distinguish the striking or main features, he sees the 
significance of the subordinate features, and he sees the past 
history and the future conditions as well as the present con- 
ditions. 

But even if we regard travel as an incident, we must recog- 
nize the fact that the World War has made us citizens of the 
world. The more we know of the world, of its natural features, 
of the laws and principles of nature, the better we are fitted 
for world citizenship. We might choose to forego pleasure or 
profit ; we cannot escape the duty placed upon us by world 
citizenship. 

Physical Geography is the science which treats of the natural 
features of the earth and their relation to life on earth. More 
than any other one subject it aims to show man his place in 
nature, his relations to his surroundings, his dependence upon 
his fellow man, upon the lower forms of life, and upon the laws 
and phenomena of nature, of which he is a part. To the ancient 
philosopher's maxim, "Know thyself," it adds: "in relation to 
nature." 



X INTRODUCTION 

The development of the science of Physical Geography in recent years, 
has led to the following subdivision of the subject : 

1. The earth as a globe or planet, and its relation to the other heavenly 
bodies 

2. The atmosphere or the surrounding gaseous portion. 

3. The hydrosphere or the water, the surrounding liquid portion. 

4. The lithosphere or solid land portions, with their various topographic 
forms, and the influence of these on climate and life. The biosphere or 
the portions of earth where life exists, is sometimes added as a fifth division. 

Physical Geography includes a study of these subjects with reference to 
their influence upon man and other forms of life. 



ELEMENTS OF PHYSICAL 
GEOGRAPHY 

CHAPTER I 
THE EARTH AS A PLANET 

1. The Earth as a Planet. — The earth is a nearly round 
ball consisting of a large rock mass partly covered with oceanic 
waters, and entirely surrounded by the gaseous atmosphere. 
The whole mass, solid, liquid, and gaseous, rotates on its axis 
as it revolves in space around the sun. It is but one of a 
number of similar bodies, called planets, and is in no wise 
conspicuous among them. It is neither the largest nor the 
smallest ; neither the farthest from, nor the nearest to, the 
sun. Because we live on the earth, it is most important to 
us, but if we could look on it from some distant point in the 
heavens we should not see anything to distinguish it particu- 
larly from the other planets. 

2. What the Solar System Comprises. — The earth is an 
important planet in the solar system, which includes the sun 
at the center, the planets and their moons or satellites, the 
very small planets called planetoids or asteroids, some planetesi- 
mal matter, such as meteorites, and some comets (Fig. 1). 
Besides the earth, there are revolving around the sun seven 
other planets, which are named in order, beginning with the 
one nearest the sun : Mercury, Venus, Earth, Mars, Jupiter, 

1 



ELEMENTS OF PHYSICAL GEOGRAPHY 



Saturn, Uranus, and Neptune. Four of these, Venus, Mars, 
Jupiter, and Saturn, are plainly visible at certain periods. 
Two of them, Venus and Jupiter, are at times the brightest 




Fig. 1. 



The solar system, showing the orbits of the planets, satellites, and 
asteroids, and of a few of the comets. 



bodies in the heavens except the sun and moon. Part of 
the time they are morning stars ; at other times evening stars. 
The planets may be distinguished from the true stars by their 
steady light. The stars twinkle. Each of the planets, except 



THE EARTH AS A PLANET 3 

Mercury and Venus, has one or more satellites or moons revolv- 
ing around it. Saturn has in addition to the satellites several 
concentric bright rings surrounding it. The relative sizes, 
distances, and other data concerning the planets are given 
in Appendix I. The student should learn to recognize the 
larger planets and observe their movements among the stars 
from season to season. 

The asteroids or planetoids^ about 600 in number, are solid bodies, 
much smaller than the planets, that revolve in orbits between Mars 
and Jupiter. One of the planetoids, Eros, about 20 miles in diameter, 
discovered in 1898, has a very eccentric orbit that sometimes brings it 
within 13§ million miles of the earth. 

3. Relation of the Solar System to the Universe. — The 

solar system, large and complex as it appears, is but one of a 
number of similar systems in the universe. Most of the bright 
stars in the heavens are suns similar to ours. They appear 
to be much smaller than our sun, but that is because they 
are so much farther away. In reality many of them are much 
larger. They probably have planets, satellites, comets, etc., 
like our own system, but they are so far away that their planets 
and satellites, if they exist, are not visible from the earth. 

It is not known how many of these systems there are, nor how far 
out into space they extend, but certainly a great distance beyond our 
comprehension. It is estimated that with a large telescope one can 
see between 100 and 200 millions of stars, a large per cent of which 
lie in the Milky Way. With few exceptions all of these stars are so 
far away that it takes the light from them, traveling at the rate of 
186,000 miles a second, many years to reach the earth. The moon is 
about 240,000 miles away, or about ten times the distance around 
the earth ; the sun is nearly 400 times farther than the moon ; and 
the nearest fixed star or neighboring sun system is several thousand 
times farther than the sun. The light of the sun takes about 8 minutes 
to reach the earth. The light of the nearest star takes 3| years to cross 
the space separating it from the earth. Truly the earth is a very small 
part of the solar system and an exceedingly minute portion of the 
universe. 



4 ELEMENTS OF PHYSICAL GEOGRAPHY 

4. The Moon. — The earth has one satellite, the moon, 
which revolves around it once a month (27.32 days) and ac- 
companies it through space in its journey around the sun. The 
moon is 2163 miles in diameter and at an average distance of 
238,840 miles from the earth, but the distance ranges from 
221,600 to 252,970 miles. It is because of its nearness to 
the earth that it is held in its orbit around the earth instead 
of pursuing an independent course around the sun. (The 
synodic month, or the time from full moon to full moon, is 29.53 
days, but the sidereal month is 27.32 days.) 

5. The Phases of the Moon. — The moon emits no light of its 
own. All the light that comes from it to the earth is reflected sun- 
light. When the moon is in that part of its orbit nearest the sun, it 




Fig. 2. — The phases of the moon. 

is nearly between the earth and the sun, and we see but a mere fringe 
of illumination ; it is then the new moon. The sunlight reflected from 
the earth faintly illuminates its dark side, giving what is called the 
earthshine. When it has completed a fourth of its circuit, after new 
moon, it is at right angles to a line connecting the sun and the earth, 
and we see one-half of the illuminated face, that is, a fourth of the 



THE EARTH AS A PLANET 



whole surface, and the phase is called the first quarter. When it has 
completed half a circuit and is on the opposite side of the earth from 
the sun, it is full moon (Fig. 2). At the third quarter the moon has 
completed three-fourths of its circuit, and one-fourth of the whole 
surface is again reflecting light to the earth. The line separating the 
illuminated portion from the dark portion is called the terminator. 
Draw from observation a figure of the moon showing the light and dark 
portion every second night from one new moon to the next ; arrange 
them in order around an ellipse and compare them. 

6. The Sun. — The sun is the center of the solar system. 
All the planets of the system revolve about it and receive heat 
and light from it. It is much 

larger than all the planets 
combined, having a diameter 
of 866,500 miles, which would 
make it a million times the 
bulk of the earth ; but since 
its density is less, it has only 
332,500 times the mass of the 
earth. Imagine the earth 
at the center of the sun and 
the moon revolving around 
it in an orbit of the same 
size as the present one ; the 
moon would then be about 
halfway from the center to 
the circumference of the sun. 
(See Fig. 3.) 

7. The Sun's Energy. — Nearly all the heat, light, and other 
forms of energy on the surface of the earth come directly or 
indirectly from the sun. The radiant energy from the sun, 
known as insolation, is thought to pass from the sun to the 
earth unaffected by intervening space until it reaches the earth, 
where part of it, the part that we recognize, is perceptible as 
heat' and light. All the energy used by man in heating and 




Fig. 3. — Diagram illustrating the rela- 
tive size of sun and earth compared with 
the moon's orbit. Diameter of the 
outer circle 866,500 miles. 



6 



ELEMENTS OF PHYSICAL GEOGRAPHY 



lighting, all that is used in running machinery everywhere, all 
that is used in lifting the waters of the sea to the clouds to fall 
as rain, all that wonderful vital energy manifested in animals 
and plants — all of these and probably other forms of energy 
as yet unrecognized are flashed like wireless telegrams across 
the vast space that separates us from the sun. Yet the part 
of the sun's insolation received by the earth is an exceedingly 
small part of the whole ; and when one realizes that this small 
part constitutes nearly all forms of heat and light known to us, 
the total quantity radiated into space is something beyond 
comprehension. 

8. Shape of the Earth. — The general shape of the earth is 
that of a sphere that is flattened at the poles and bulged at 
the equator, so that the equatorial diameter is nearly 27 miles 
longer than the polar diameter. It approaches an oblate 
spheroid more nearly than any other mathematical figure. 



Evidence that the earth, has a curved and not a flat surface : (1) Its 
shadow on the moon is always a curved one. Could this be true of a 

flat surface ? (2) New 
^A stars appear in front 

of the observer and 
old ones disappear 
behind him as he 
travels north or 
south. How would 
it be on a flat surface ? 
(3) The horizon ex- 
pands rapidly as the 
observer ascends to 
higher altitudes. (See 
Fig. 4.) Would this 
be true on a flat sur- 
face? (4) At sea the 
slender toprigging of a vessel is visible farther than the larger but 
lower hull. Why? (5) There is a marked difference in time with a 
change of longitude ; thus the sun rises more than three hours later 




Fig. 4. — Expansion of the horizon with elevation 
indicates curvature of the earth's surface. 



THE EARTH AS A PLANET 7 

in San Francisco than it does in Philadelphia, and more than eight 
hours later than it does in London. How would it be if the earth were 
flat? (6) The earth has been circumnavigated many times. (7) The 
flattening at the poles is indicated by the increased weight of a body 
in high latitudes over the same body at the equator, and by the 
greater length of a degree of latitude near the poles. (See Sec. 21 
and Fig. 9.) 

9. Size of the Earth. — The diameter of the earth through 
the poles is 7,899.6 miles; through the equator, 7,926.6 miles. 
Compute the circumference, the area, the volume, and the 
weight of the earth in tons from the following data. 

(1) The circumference equals the diameter multiplied by 
3.14159. 

(2) The area equals the product of the diameter and the cir- 
cumference of a great circle. 

(3) The volume equals the area of the surface multiplied by 
one-third of the radius. 

(4) The mass equals the volume multiplied by the density. 
The mean density of the earth is 5.6. A cubic foot of water 
weighs 62.5 lbs. 

10. Problem of Eratosthenes. — The diameter of the earth was 
not the dimension first determined, as there is no way of measuring it 
directly. The part that was actually measured was an arc of the 
circumference. This problem was first solved by Eratosthenes two 
centuries before the Christian era. He determined that Syene in 
Egypt was close to the same meridian, hence to the same great circle, 
as Alexandria. He had observed that at noon on the longest day in 
midsummer the sun's rays shone on the bottom of a deep well near 
Syene in Egypt. What inference could he draw from this? He 
measured the angular distance of the sun from the zenith at Alexandria 
on the same day at noon and found it equaled 7 degrees and 12 minutes, 
or exactly one-fiftieth of a circle, which is the same as the angle at 
the center of the earth formed by the radii from these cities. Prove 
this. The distance between the two cities had been measured and 
found to be 5000 stadia, hence by multiplying this distance by fifty 
he obtained the total distance around the earth as 250,000 stadia. 



8 ELEMENTS OF PHYSICAL GEOGRAPHY 

Unfortunately we have no means of knowing at the present time the 
length of a stadium of that day in any of our units of measurement, 

so that we have no certain 
Z,,,,, Z' means of comparing the 

accuracy of the result ob- 
tained by Eratosthenes 
with those obtained by 
similar means in more re- 
cent times. (See Fig. 5.) 




11. Structure of the 
Earth. — The earth is 
frequently divided for 
convenience of study 
into three parts or 
spheres : (1) The outer 

Fis. 5. — Illustrating the problem of Eratos- gaseOUS envelope, the ol- 

thenes. The sun's rays vertical at A are in- i . (<y\ |U P ]\ m -.\A 

clined 7° 12' to the vertical SZ' at S, which is mos P nere > W tne liquid 

the angle of the two radii at the center of the envelope, the water or 

earth, C, measured by the arc AS. This is one- h v( 1ro<i<nhere whirh 

fiftieth of the circumference of the circle which "»"' ut >P n(i ' 6 > WIUCI1 

is the circumference of the earth. nearly surrounds (3) the 

solid rocky part, the 
lithosphere, the inner portion of which is sometimes called the 
centrosphere. A fourth is sometimes added, called the biosphere, 
or life sphere. These are not true mathematical spheres, nor 
are they very sharply separated. Both the hydrosphere and 
the atmosphere penetrate the lithosphere ; large quantities of 
the atmosphere are dissolved in the hydrosphere, and large 
quantities of water occur as invisible vapor in the atmosphere. 
The life is confined chiefly to the water and the surface of the 
land. It is scattered through the water sphere to a greater 
depth, probably, than in either the gaseous or rock portions, 
yet the greater portion of it lies close to the lower portions of 
the atmosphere. The air, water, and land portions of the 
earth, which form the greater part of the subject of physical 



THE EARTH AS A PLANET 9 

geography or physiography, are discussed in the following 
chapters. 

12. Motions of the Earth. — The earth has (1) a daily 
rotation on its axis, and (2) a yearly revolution around the sun. 
Besides these it has (3) an onward motion through space in 
company with the other parts of the solar system, but this is 
not so apparent as the other two and is not marked by such 
pronounced effects. There are a number of other minor motions 
of interest to the astronomer. 

13. Rotation. — The rotation of the earth on its axis causes 
the sun and the stars to appear to revolve about the earth. 
Thus, the sun appears to rise in the east and set in the west, 
producing the successive changes of day and night and giving 
the measure of time, the day. The rotation of the earth is 
one of the factors, in producing the tides and the belts of 
planetary winds and calms; and it affects the direction of 
the ocean currents. The rotation also produces the bulging 
at the equator and the flattening at the poles. It causes a 
deflection of falling bodies. A ball dropped from the top of a 
tower would be deflected to the east of the base of the tower, 
instead of falling directly vertical. The deviation is greatest 
at the equator and zero at the poles. Why? In the latitude 
of New York it is about one inch for a fall of 500 feet. This 
deflection would be taken into consideration by the aerial 
navigator in the European War in dropping bombs or other 
objects from elevations of thousands of feet. 

14. Foucault's Pendulum. — In the middle of the last century 
Foucault demonstrated the rotation of the earth by means of a pen- 
dulum consisting of a heavy weight suspended on a long slender cord 
which is started to swing due north and south across a plane surface 
covered with fine sand. Attached to the bottom of the pendulum is 
a sharp point which traces a mark in the sand as it swings. If the 
earth were still, the pendulum would continue to swing on this line ; 
but the rotation causes this plane under the pendulum to rotate to 



10 ELEMENTS OF PHYSICAL GEOGRAPHY 

an extent varying with the latitude, from zero at the equator to a com- 
plete revolution at the poles. This is shown by the lines in the sand 
made by the pendulum. 

15. Directions. — The terms north, south, east, and west 
are used to signify directions on the surface of the earth and 
ajso in space. North with reference to the earth really means 
the direction of the north pole, one end of the axis of the earth, 
and is a curved line corresponding to the meridian at the point 
where the direction is taken. What we really think of, how- 
ever, is the line on the plane of the horizon which marks its 
intersection with the plane of the meridian. North in the 
heavens refers to the direction of the axis of the earth prolonged 
to infinity passing nearly through the north star. At a point 
on the equator this direction is identical with north on the 
earth, but as one approaches the north pole the two lines diverge 
until- near the pole they are nearly at right angles to each other. 
Represent this by a diagram for (1) your latitude, (2) the 
equator, and (3) the north pole. 

At the north pole all directions on the horizon are south, and 
the line to the north star is perpendicular to the horizon. At 
all other points on the earth, south is the opposite direction 
from north until one arrives at the south pole, where there is 
no south, but all directions are north. 

East and west refer to the directions on the horizon at 
right angles to the north and south line. East is to the right 
as one faces north, west to the left. If followed, the east and 
west line proves to be a curved line. The equator and the 
parallels of latitude are east and west lines, yet they are 
circles on the globe. The terms east and west are used for 
directions of rotation and revolution ; thus the earth rotates 
toward the east, because any one point on the earth at any 
instant is moving east in the plane of the horizon. 

The plane of the horizon is the plane perpendicular to the plumb 
line. The point where the extension of the plumb line pierces the 



THE EARTH AS A PLANET 11 

heavens is called the zenith and the direction is up. The point opposite 
the zenith is the nadir and the direction is down. 

The ancient peoples did not believe that the earth was round be- 
cause they could not see why people on the opposite side would not 
fall off. They were unacquainted with the law of gravity. They 
did not know that all bodies on the surface are held there by the force 
of gravity, that everywhere over the surface of the earth dg^xa—i»~ 
towards the center of the earth, because that is the center of gravity. 
The measure of this force we call weight. A body weighing ten pounds 
is pulled by gravity toward the center of the earth with ten times the 
force of one weighing one pound. 

16. Revolution of the Earth. — The revolution of the earth 
around the sun causes the latter to appear to shift its position 
in the heavens from day to day. In connection with the in- 
clination of the earth's axis and the rotation of the earth on its 
axis, the revolution helps to cause the change of seasons. The 
earth travels around the sun in an elliptical orbit with the sun 
at one focus of the ellipse. At the nearest point (perihelion) 
it is about 91,500,000 miles distant ; at the most remote point 
(aphelion) it is about 94,500,000 miles away. The inclination 
of the earth's axis to that of the axis of the ecliptic of the 
earth's path around the sun is 23 degrees 27 minutes, which 
means that the plane of the earth's equator is inclined at 
the same angle to that of the plane of the ecliptic. This 
inclination remains fixed (or nearly so) with reference to space 
and distant stars in the heavens, so that the axis of the earth 
with slight variations always points approximately to the 
same star in the heavens, but it causes the earth to assume 
quite different positions with reference to the sun, as shown in 
Fig. 6. 

17., The Seasons. — On December 21st the northern hemi- 
sphere reaches its maximum inclination from the sun, the 
vertical rays of the sun are on the Tropic of Capricorn, their 
southern limit, and it is then the winter solstice. The area 
around the north pole is in darkness, and it is winter in the 



12 



ELEMENTS OF PHYSICAL GEOGRAPHY 



northern hemisphere, while the area around the south pole is in 
continual sunshine, and it is summer in the southern hemi- 
sphere. The opposite condition prevails on June 21st, the 
summer solstice, when the northern hemisphere is inclined 





Wjl/ 




Fig. 6. — The seasoas. 

toward the sun and the rays are vertical on the Tropic of Cancer. 
It is then summer in the northern hemisphere and winter in 
the southern. On March 21st and September 22d the axis 
of the earth is perpendicular to the line joining the center of 
the earth and the center of the sun, and the sunshine extends 
from pole to pole, so that the days and nights are equal (the 
equinoxes). Name the corresponding seasons. 

Winter in the northern hemisphere does not come when the earth 
is farthest from the sun, but when it is near perihelion, and the summer 
season comes when it is near aphelion, showing that the few degrees 



THE EARTH AS A PLANET 13 

difference in the angle at which the sun's rays strike the earth have a 
greater influence on the temperature than the three millions of miles 
difference in distance. The heat of summer and the cold of winter are 
increased by reason of long days and short nights in the summer and. 
long nights and short days in the winter. 

Every place on the earth's surface has the same number of hours 
of daylight and darkness in a year as every other place, but the dis- 
tribution of the light and darkness is different. Thus, within the 
tropics there is little variation from 12 hours light and 12 hours dark- 
ness for each day in the year, but beyond the tropics there is a gradual 
change in the relative length of day and night during the different 
seasons, until one reaches the poles, where they are again equal, but 
each day is six months long and there is but one day and one night 
in the year. 

The space between the sun and the earth is dark and cold and the 
sun's rays are changed to heat only after reaching the earth and the 
earth's atmosphere, and those that reach the earth at a low angle, as 
at and near the poles, are largely reflected off without producing much 
heat. Hence, while the polar regions receive as much sunshine as the 
equatorial regions, they receive much less heat from the sun. 

If the axis of the earth were perpendicular to the plane of the 
ecliptic, what would be the effect on the seasons? What would be 
the effect on the winter and summer of New York State if the axis 
were inclined twice as much as at present? The axes of some of the 
other planets are inclined much more than the earth's. (See Ap- 
pendix I.) 

LATITUDE AND LONGITUDE 

18. Location of Places. — The relative position of any two 
points on any surface may be expressed in distances in two 
directions at right angles. If stated in one, it can readily be 
analyzed into two. If stated in two, they can readily be com- 
bined into one. The directions and distances may be expressed 
in various units, but the principle is the same. 

In the city, you are told that Brown's store is two blocks 
east and two north. In the country, Brown's house is two 
miles east and two north. On the ocean, Brown's ship is 
two degrees east and two north. The principle is just the same 



14 



ELEMENTS OF PHYSICAL GEOGRAPHY 



in all three instances, but the units are different. The last we 
call latitude and longitude, but the others are just as much so, 
and all involve length and breadth, which are common to all 
surfaces. 

It makes no difference how the area is bounded or whether it is 
bounded at all, if two lines cross each other as BD and EC at A (Fig. 7), 
a point X may be definitely located anywhere with reference to the 



1 xT 

%, 3Ei, 

L> 

1 4 



D 

Fig. 7. — Illustrating the location of points on a surface. Any point is 
readily located with reference to A, a point where two lines BD and EC cross 
each other. For example, Z is one east, two north, S is two east and one south. 

known point A by stating the distances on the north-south line BD 
and the east- west line EC. Thus X would be two east and three north. 
It may be two inches, two feet, two blocks, two miles, or two degrees. 
If stated in degrees, we think latitude and longitude, but the others 
are just as much so. 

19. Latitude and Longitude. — Distances north and south 
on the surface of the earth are called latitude, distances east 
and west longitude; latitude and longitude are commonly 
expressed in degrees and fractions of a degree. Any line of 



THE EARTH AS A PLANET 



15 



direction on the surface of the earth if extended forms a circle 
around the earth. Any circle the diameter of which passes 
through the center of the earth is a great circle, all others are 




SouihPolr Meridians af £.6n4ifiu/e South Pole 

Fig. 8. — Parallels and meridians. 

small circles. All north and south lines, called meridian circles, 
pass through the poles and hence are great circles. The east 
and west circle midway between the poles is called the equator. 
It is the only east-west circle that is a great circle ; all the 
others are small circles and are called parallels of latitude 
(Fig. 8). 

2Q. Length of Degrees. — Since all circles are divisible into 
360 parts, named degrees, it follows that degrees in large circles must 



16 



ELEMENTS OF PHYSICAL GEOGRAPHY 



be longer than those in small circles. The equator is a great circle, 
7926.6 miles X 3.14159, or 24,902 miles, in circumference. Each degree 
on the equator is 24,902 divided by 360, or 69.17 miles long. The 
parallels of latitude north and south of the equator are successively 
shorter towards the poles. Hence the length of degress of longitude, 
which are measured on the parallels, decreases from 69.17 miles at 
the equator to zero at the poles. At 60 degrees north or south latitude 
the degree of longitude is 34.914 miles long. 

21. Latitude. — Latitude is measured north and south from 
the equator on the meridians, which are all great circles, and 

the degrees of latitude would all be 
the same length if the meridians were 
perfect circles. It has been stated 
(See Sec. 8) that owing to rotation the 
earth is flattened somewhat at the 
poles and bulged at the equator, which 
would make the degrees a little longer 
near the poles and a little shorter near 
the equator, but the difference is not 
great. 69.407 miles is the length of a 
degree at the poles and 68.704 miles at 
the equator (Fig. 9). 

Latitude is measured north and 
south from the equator to the poles. 
Since the equator bisects each meridian 
circle and the poles again bisect each 
half circle there can be only a fourth 

of 360 degrees, or 90 degrees, north latitude and likewise 90 

degrees south latitude. 

22. Longitude. — Longitude is measured east and west on 
the parallels. In order to locate definitely any point on the 
earth one of the meridians must be chosen as a starting point, 
which is zero longitude. Since the meridians are all great 
circles and all similar, any one of them may be chosen as the 
zero or prime meridian. 




Fig. 9. — Degrees of lati- 
tude are longer at the poles 
than at the equator because 
they are measured by the 
arc of the curve of the sur- 
face, and the flattening at 
the poles makes the curva- 
ture of a greater circle than 
at the equator. 



THE EARTH AS A PLANET 17 

Formerly it was customary for each nation to select the 
meridian passing through'its capital city for its prime meridian. 
The United States reckoned longitude east and west from the 
meridian passing through Washington, France from the Paris 
meridian, and England from the London meridian, or rather 
from the one passing through the Royal Observatory in Green- 
wich, near London. It would save the necessity of designating 
the name of the meridian each time if all nations would agree 
to use the same principal, or prime, meridian. Without any 
official agreement, nearly all civilized nations have gradually 
accepted and use the Greenwich meridian, because England 
has the greatest commerce and London has been the center 
of the world's commerce. Hence the longitude record of any 
place, when not otherwise qualified, means that it is reckoned 
from the Greenwich meridian. Where the Greenwich meridian 
crosses the equator is zero latitude and longitude. Longitude 
10° E. and latitude 20° N. means that the point is 10 degrees 
east of the meridian of Greenwich and 20 degrees north of the 
equator. 

23. Determination of Latitude. — At sea the latitude is 
generally determined by finding the altitude of the sun by 
means of an instrument called the sextant. There are several 
different ways in which it can be determined on the land with- 
out the use of a sextant or any other expensive instrument. 
The north star is very nearly vertical over the north pole, 
hence its altitude over that point is 90 degrees. At the equator 
the north star would appear on the horizon, that is, its alti- 
tude would be zero. Hence the altitude of the north star 
above the horizon gives the latitude of any place in the 
northern hemisphere, subject to a slight correction (Fig. 10) . 

At the times of the equinoxes, March 21 and September 22, the 
sun is on the equator, where a person at noon on the dates mentioned 
sees the sun directly overhead or at an altitude of 90 degrees, and a 
person at the north pole at the same time sees the sun on the horizon. 



18 



ELEMENTS OF PHYSICAL GEOGRAPHY 













fe 


a 








55 


w 








i 


■S 




s 







o 




to 




Z 



z 

.0 




3 


u 


H 
k 'J. 


i s 






Z 

|2 










z 




1 


/ ° 


12 




1 


$7 


N^, 

X 


o 








?J>\ 




c 







Hence on the dates mentioned the altitude of the sun at midday, 
when subtracted from 90 degrees, gives the latitude of the place. 

On any other day in the 
year, the same method 
may be followed by the 
subsequent addition or 
subtraction of the sun's 
angular distance from the 
equator. This can be ob- 
tained for any day in the 
year by consulting a nau- 
tical almanac. In this 
method care must be taken 
to get the altitude of the 
sun when it is on the 
meridian or the true north 
and south line, which may 
be determined by means 
of a magnetic needle or 
compass and the correc- 
tion made for the local 
magnetic variation ; or at 
night by noting and mark- 
ing carefully the direction 
of the north star ; or by 
noting the direction of the sun's shortest shadow cast by any vertical 
post. 

24, Determination of Longitude. — Longitude is determined 
by finding the difference in time between the place in question and 
the meridian of Greenwich or some point whose longitude is known. 
Since the earth rotates on its axis once in 24 hours, in one hour a 
point on the surface must go 5 ? of 360 degrees or 15 degrees, or one 
degree in four minutes. Hence the difference in time expressed in 
hours multiplied by 15 will give the difference in longitude expressed 
in degrees. For example, a place two hours west of Greenwich is in 
2 X 15, or 30 degrees, west longitude. Longitude is commonly de- 
termined by a chronometer or by telegraph. Thus, if one has a 
chronometer which records Greenwich time, it is only necessary to 
determine carefully the time by this chronometer when the sun crosses 
the meridian at the point to be determined and multiply the difference 



Fig. 10. — Determination of latitude from 
observations of the north star; hh, h'h', etc., 
plane of the horizon. At the equator, E, the 
star appears on the horizon, elevation and lati- 
tude zero. At 40° north latitude the elevation 
of the star is 40°. Hence the elevation of the 
north star at any point equals the latitude of 
the place. 



THE EARTH AS A PLANET , 19 

between this time and 12 o'clock, by 15, to have the longitude of the 
place. By the other method, if a person in Buffalo should telegraph 
to St, Louis the exact time when the sun is on the meridian at Buffalo 
and the person in St. Louis subtracts this from the time the sun is on 
his meridian and multiplies the result by 15 (if in hours, or divides by 
4 if in minutes), he would have the difference in longitude between the 
two places. For accuracy, an addition or subtraction must be made 
for the equation of time (Sec. 27) obtained from the Nautical Almanac. 

25. Use of Latitude and Longitude. — All globes have some 
parallel and meridian lines marked on them for convenience 
of locating any point desired. The same is true of maps of the 
world and of the hemispheres, and on all government maps 
of even small areas. While only a few lines are drawn, it is 
understood in all cases that the spaces between the lines can 
be subdivided as much as desired. Each degree is divisible 
into 60 parts called minutes and expressed by a mark resembling 
an apostrophe, thus 30'. Each minute is divisible into 60 
parts called seconds, designated by a double mark, thus 30", 
and each second is divisible into whatever fractions are desired. 

Latitude and longitude are the only means by which a ship 
is located at sea. Thus, when a ship at sea is in distress and 
sends out a wireless call for help, the officer always gives the 
latitude and longitude as definitely as he has determined it. 
It is by frequent determination of the latitude and longitude 
that the officer of the vessel keeps track of his position at sea 
and avoids islands, shoals, and other danger points. 

While latitude and longitude are indispensable in navigation, 
they are just as useful on the land. City streets, highways, 
railways, pipe lines, land boundaries are all based fundamentally 
on latitude and longitude, but the determination and measure- 
ment of distance and direction are different from those em- 
ployed at sea, and they are generally expressed in different terms. 

26. Use of Latitude and Longitude in Public Lands. — All of 

the public lands of the United States west of Pennsylvania were laid 



20 



ELEMENTS OF PHYSICAL GEOGRAPHY 



out in rectangular blocks based, more directly on latitude and longitude 
than the land lines of the eastern states. In this method an east- 
west line or parallel, measured and marked with care, is called a base 



R.2W. R.l 


W. 


Kl 


E. R.2E. 
T. IN. 




6 


5 


4 


3 


2 


1 




Base Line 


7 


8 


9 


10 


11 


12 


18 


17 


16 


15 


14 


13 


W, 


20. 


21 


22 


23 


24 


30 


29 


28 


27 


26 


25 


31 


32 


33 


34 


35: 


36" 




' 


Hfl. 

i 

■a 


T.1S. 






m 
gi 

a 


T.2S. 



Fig. 11. — Diagram illustrating the use of latitude and longitude in dividing 
lands. The initial parallel is called a base line, the other parallels 6 miles apart 
are township lines. The meridian lines east and west of the first principal 
meridian are called range lines. The mile-square sections are marked in 
T. 1 N., R. 1 W. 



line. A north-south line or meridian is measured and marked as a 
principal meridian. Other parallels are then measured north and 
south of the baseline and are marked T. 1 N., T. 2 N., T. 1 S., T. 2 S., 
etc., meaning township 1 north of the base line, etc. These east- west 
lines are six miles apart and called township lines. Other north- 



THE EARTH AS A PLANET 



21 



south or meridian lines are measured in a similar manner at six-mile 
intervals from the principal meridians (P. M.) and called range lines 
(R. 1 W. of P. M., R.2W, etc.)- These lines block out the area 
in plots 6 miles square, called townships. (See Fig. 11.) 



N.K Sec. 16 




320 A. 




Sec. 16 




S. W.M of Sec. 16 
160 A 


N W. % 

of ' 

N.W. % 

°> . 
S. E. 'A 


10 A 


40 A 


















s. w. x 


S. E. X 




of 


of 




S. E. % 


S.E. % 



Fig. 12. — Diagram illustrating the subdivisions of a section. 



The townships are subdivided into plots a mile square by running 
parallels and meridians a mile apart. The mile-square plots are called 
sections and contain 640 acres each. These are again subdivided into 
quarter sections of 160 acres by parallel and meridian lines crossing 
in the middle of the section. The quarter section is further divided, 
when desired, by another parallel and meridian into four plots of 40 
acres each. This subdivision could be carried on indefinitely if de- 
sired." (See Fig. 12.) 



22 ELEMENTS OF PHYSICAL GEOGRAPHY 

Each township 6 miles square contains 36 sections each a mile 
square. These are numbered from 1 to 36 by beginning at the 
upper right corner and numbering back and forth to 36 in the lower 
right corner, as shown in the diagram. A 40-acre farm in the lower 
right corner of section one of the first township north and west of 
the base line and first prime meridian, would be designated as the 
S. E. I of the S. E. \ of Sec. 1, T. 1 N., R. 1 W. In a similar manner 
any farm on lands so surveyed may be located definitely, so that a 
person in another country knows its exact location on the map, if he 
understands the system, just as a mariner at sea knows the location 
of a ship or an island when he has the latitude and longitude. Dif- 
ferent names are used, but the principle is the same. 

The pupil should study the diagrams (Figs. 11 and 12) until he 
can quickly designate the location of any section, quarter section, or 
40-acre tract on the plot. 

In practice there are irregularities in these land plots due to errors 
in surveying. Many of the townships, accordingly, are not six miles 
square and some of the sections are more and some less than a mile 
square. As far as possible these irregularities are placed in the sec- 
tions along the north and west sides of the township. 

Before the above uniform system of surveying public lands was 
adopted by the government, some townships in Ohio were surveyed 
in which the sections were numbered north and south through the 
township instead of east and west. (See the Chesterhill, Ohio, 
quadrangle.) 



TIME 

27. The Day. — The sidereal day is the length of time it 
takes the earth to make a complete rotation with reference to 
a star, that is, until the star is again vertical over the same 
meridian. 

The solar day is the time of rotation with reference to the 
sun. Suppose the sun and a star on the meridian at the same 
time ; during the interval until the star is again on the meridian, 
the sun will lack 3 min. 56.55 sec. of being there owing to the 
forward movement of the earth in its orbit. Hence the solar 
day is that much longer than the sidereal day. 



THE EARTH AS A PLANET 23 

But solar days are not all the same length, owing to the fact that 
the earth moves more rapidly in some portions of its orbit than in 
others. Since it is not possible to construct a clock that will follow 
all variations of the sun from day to day, the length of our day is 
based not on the real sun, but on a mean sun, moving through the 
heavens at the average rate of the true sun. This is called mean 
solar time, which is the time measured by our clocks. The difference 
between the true solar time and the mean solar time is known as the 
equation of time and may be found in the almanac frequently marked 
sun fast or sun slow. It should be noted that even the mean solar 
day is actually determined by computation from the sidereal day. 

The civil day begins and ends at midnight rather than at 
noon, as a matter of convenience. For the same reason the 
astronomical day begins at noon. It is also a matter of con- 
venience to have a fixed place where the day changes, or one 
day leaves off and another begins. 

The Conventional Day. — It is always apparent noon on the 
meridian under the sun in its apparent passage around the earth. 
In imagination if we should follow the sun from noon on Monday 
around the earth until we returned to the starting point after 24 hours, 
it would have been noon all the time, and the question arises, " Where 
did we pass from Monday to Tuesday?" This place for the change 
of date was at one time fixed at the 180th meridian east or west from 
Greenwich, that is, on the opposite side of the earth from the prime 
meridian, so that vessels crossing this line added or subtractsd a day, 
depending on which way they were going. It was found that the 
180th meridian extended through groups of islands belonging to the 
same nation, so that it was found advisable to shift it enough to have 
it come between nations and yet vary as little as possible from its 
first position. It is now called the international or intercalary date line 
and is shown on Fig. 14. The day which changes here is known as 
the conventional day ; that is, the day which is added or subtracted 
as one crosses the line. 

The lunar day is the interval between successive passages of the 
moon across the meridian, and is nearly an hour (52 minutes) longer 
than the solar day. 

In both the sidereal day and the astronomical day, the hours are 
numbered from 1 to 24, thus avoiding the repetition of a.m. and p.m. 



24 



ELEMENTS OF PHYSICAL GEOGRAPHY 



This method of numbering the hours is used on the railwaj^s in some 
countries. Why is it not used in the United States? 

28. Standard Time. — If every place on the earth kept its 
time by the sun accurately, it would lead to a constant change 
of time as one traveled east or west. This was found to be so 
confusing on the railroads that some years ago a standard time 




Fig. 13. — Map of standard time belts of the United States. Compare with 
one of a few years ago and note how the boundaries have changed. 

was adopted, in which instead of changing the time every 
minute or second, or at every town, it is changed only once an 
hour, and on the even hours from Greenwich. Thus, in the 
Eastern United States the time is based on the 75th meridian, 
or the one passing through Philadelphia, which is five hours 
west of Greenwich. Further west it is based on the 90th or 
St. Louis meridian, the 105th or Denver meridian, and the 
120th or the one passing on the boundary between California 



THE EARTH AS A PLANET 25 

and Nevada. The time, however, does not change on these 
meridians, as by so doing it would give the place immediately 
west of the line time nearly an hour different from sun time ; 
so, to make the difference from sun time as little as possible, 
the change of time should be midway between the standard 
meridians ; but for various reasons the first location of the time- 
belt boundaries was far from the medial line. In January, 
1919, while the government had control of the railways, the 
boundaries were shifted so as to equalize more nearly the 
width of the different belts. (See Fig. 13.) 

The different names given to these time belts from east to 
west in the United States are Eastern, Central, Mountain, and 
Pacific time, and they are respectively 5, 6, 7, and 8 hours 
slower than Greenwich time. The accurate standard time is 
sent regularly at twelve o'clock each day from the naval ob- 
servatory at Washington to all the important telegraph offices 
in the United States. Standard time similarly determined is 
used on the railways in most of the European countries. 

France adopted the standard time based on the Greenwich meridian 
in 1911. In order to make as little confusion as possible in the in- 
dustrial world the change was made late at night. On the night of 
March 10th, 1911, all the railway trains and all watches and clocks 
were stopped for 9 minutes and 21 seconds (the difference between 
Paris and Greenwich time), and thus was avoided any change in the 
railway schedules. 

In 1917 the French Navy adopted Greenwich standard time belts 
at sea. Probably other nations will in time adopt the same plan and 
the twenty-four standard hour time belts will be recognized around 
the world. This will be another recognition of the unity of the peoples 
of the world. Steamship lines connect all nations, railway lines and 
telegraph and telephone lines cross international boundaries. Soon 
aerial lines will do the same. All of these tend to unite more closely 
the peoples of all lands into a brotherhood of nations. 

World-wide standard time is but a recognition of expanding com- 
merce -and travel brought about by the increase and improvement in 
lines of communication, which are breaking down the stone walls and 



26 ELEMENTS OF PHYSICAL GEOGRAPHY 

forts of international boundaries. Even now there are people in 
New York City and Boston that know more about London and Paris 
than they do about Denver and San Francisco. 



MAGNETISM 

29. Magnetism. — Magnets are bodies which have the 
power of attracting iron and of being in turn attracted by 
iron; in a much less degree the metals manganese, cobalt, 
and nickel also attract and are attracted thus. Magnets are 
natural and artificial. The natural magnet is the mineral 
lodestone, a variety of magnetite. A piece of hardened steel 
may be made into a permanent magnet by rubbing it on a 
piece of lodestone, or better, by placing it inside of a wire coil 
and subjecting it to a strong electric current. If the piece of 
magnetized steel or piece of lodestone be now freely suspended 
on a pivot, it will form a magnetic needle, which, properly 
mounted, forms the mariner's compass. In the absence of a 
pivot it may be floated on a cork in a vessel of water. 

30. The Earth a Magnet. — If two compass needles are brought 
near each other, it will be seen that the north end of one repels the north 
end of the other, but attracts the south end. From this and other 
observations it is thought that the earth itself is a great magnet and 
that the poles of the great earth magnet are near, but not at, the 
north and south poles of the earth. The north magnetic pole lies 
in the region north of Hudson Bay and west of Baffin Bay. Recent 
studies seem to show that it is not a fixed point, but an area of con- 
siderable size. The north end of the compass needle points toward 
this magnetic pole, not the true north pole ; hence in northern Green- 
land, the compass needle points south of west instead of north. In 
only a few places does the magnetic needle point to the true north, 
and these points are connected by lines known as agonic lines. At 
all other points the needle varies from a true north direction, which 
variation is known as the magnetic variation or declination. Points 
having the same declination are connected by a line called an isogonic 
line. Note the position of the agonic and isogonic lines on Fig. 14. 



THE EARTH AS A PLANET 



27 




28 



ELEMENTS OF PHYSICAL GEOGRAPHY 



Midway between the magnetic poles is the magnetic equator, 
where a needle suspended to swing in a vertical plane lies horizontal. 
As the needle is taken north from the magnetic 
equator, the north end dips below the horizontal 
until a point directly over the magnetic pole is 
reached, where it stands vertical. A needle so sus- 
pended as to swing freely in a vertical plane is called 
a dipping or dip needle, and lines connecting points 
where the angle of dip is the same are isoclinal 
lines. (See map, Fig. 14, and Fig. 15.) The isoclinals 
appear to be very nearly parallel with the isotherms, 
which would indicate some possible relation between 
the earth's magnetism and the heat on the surface. 
It is thought that in some way the rotation of the 
earth is a cause or the cause of its magnetism. 




Fig. 15. — 
Dipping needle 
in position near 
south magnetic 
pole. 



31. Importance of the Compass. — The discovery and use 
of the magnetic compass probably did more toward the civiliza- 
tion of the world than anything else in the world's history. It 
not only furnished a key to travel and exploration of all parts 
of the world, but led to system and unity in man's efforts on 
land as well as on the sea. The compass is used in laying out 
lines on both sea and land. Our railways, highways, pipe 
lines — all our lines of communication are based on the magnetic 
compass. The boundaries of farms and land areas of all kinds 
are determined by the use of the compass. 



MAPS AND MAP PROJECTION 

The representation of the different geographic features of the 
earth's surface on paper has been tried in a great many dif- 
ferent ways, in order to gain accuracy combined with ease and 
rapidity of construction and economy of duplication. 

32. Globe. — The ordinary globe shows all features in their 
true horizontal relations better than any other method, but it is 
too expensive and too inconvenient for most purposes. A 
globe on which the mountains and plateaus are shown in relief 



THE EARTH AS A PLANET 29 

and the ocean basins shown by depression is more realistic and 
likewise more expensive. 

33. Model. ■ — Next to the globe, a model or relief map con- 
structed of plaster, clay, or papier-mache is one of the best 
ways of showing the surface features. A model may be made 
of the entire globe, but more commonly it is made of some 
small portions only, which can thus be shown on a larger scale. 
The advantage of the model is that it shows vertical as well 
as horizontal relations, but the objections are the expense of 
construction and duplication and the inconvenience in carrying 
about or storing for reference. 

34. Maps. — Maps in which the features are shown on the 
surface of thin paper are much more convenient to handle and 
store away, and much less expensive than either globe or model. 
Hence there are hundreds of times as many maps in use as 
models or globes. 

35. Projections. — Since the earth is spherical in form, the 
attempt to represent its surface on flat paper is attended with 
more or less distortion. A curved area spread out flat necessi- 
tates crumpling in some places and stretching in others. To 
overcome this difficulty various methods have been devised 
for projecting the lines of the curved surface upon a flat one. 
Some of the various methods employed are described in Ap- 
pendix II. 

36. Scale of the Map. — The scale means the ratio of the dis- 
tances between points on the map and the corresponding points on 
the earth. It may be given in units, such as, 1 inch equals 1 mile, 
or by fractions, ss^es or 1 : 63,360, which means that one inch on the 
map corresponds to one mile on the earth. The scale used in the 
construction of a map depends on the size of the area to be mapped, 
the purpose for which the map is wanted, and the money available for 
its construction. An increase in the scale means an increase in the 
cost of construction. Many of the contour map sheets published by 
the United States Geological Survey are on a scale of 1 : 62,500, but 
some have a scale of 1 : 125,000 and some 1 : 250,000, while others have 



30 ELEMENTS OF PHYSICAL GEOGRAPHY 

a smaller scale. Maps of the whole United States have a much 
smaller scale, some being 1 : 2,500,000, some 1 : 7,000,000, and still 
others 1 : 14,000,000. The scale should always be marked on a map, 
either by ratios or graduated lines, or in both ways, except on small- 
scale maps of large areas, where the latitude and longitude lines in- 
dicate the scale. The governments of a number of the civilized nations 
of the world have now agreed to map their own areas on a uniform 
scale of 1 : 1,000,000. The United States has already published 
several sheets of this international map of the world. 

37. Contour Maps. — Elevations and depressions on the 
surface of the earth may be represented on the maps by (1) shad- 
ing, (2) contour lines, and (3) hachures or broken lines. 

The model or relief map shows to the eye the features of re- 
lief better than any plan yet devised to show the same on a 
map. Of the different methods in use for representing relief 
on a flat surface, shown in Fig. 16, the contour map is superior 
for many purposes. The hachures and the shading show hills 
and valleys, but they do not show the height of the hills or the 
depth of the valleys. The contour map shows not only the 
relative, but the actual, elevation of any and every point on 
the area. 

The map is constructed by drawing lines connecting all 
points that have the same elevation above sea level. (Any 
known point may be taken as a base, but sea level is generally 
taken for convenience.) The number of contour lines drawn 
on the map varies with the regularity of the slopes, the scale 
of the map, the height of the hills, and the amount of detail 
desired in the map. The vertical distance between the lines, 
known as the contour interval, is sometimes 2, 5, 10, or 20 feet 
on a large scale map of a small area without high hills. In a 
mountain district the interval is 50, 100, 500, or 1000 feet. 
(State the reasons why an interval of 5 feet is used on the 
Donaldsonville, Louisiana, topographic sheet, and 100 feet on the 
Charleston, West Virginia, sheet.) 

On the United States Geological Survey maps the contour 



THE EARTH AS A PLANET 



31 




Fig. 16. — Illustrating methods of showing relief by (1) shading, (2) contour 
lines, (3) hachures. The method by contours is the only one that shows actual 
elevation of all points. 



32 ELEMENTS OF PHYSICAL GEOGRAPHY 

lines are printed in brown to avoid confusion with streams, 
roads, and other lines. 

The first contour line (which is generally not in brown) on 
any continent or island area is the one marking the separation 
between the land and the sea ; that is, the one marking the 
contour of the land. The second line would mark the contour 
of the land if the water should rise ten feet (or the space of the 
contour interval), and so on. If one considers the contour lines 
as marking the water level at successive stages, the significance 
of the name becomes apparent. A contour line never ends 
except at the margin of the map. On a map of an island or of 
an entire continent all contour lines are continuous. 

38. The United States Topographic Atlas. — The United 
States Geological Survey contour map sheets in the Topographic 
Atlas of the United States will in time cover the entire area of the 
country on a scale of approximately one, two, or four miles to the 
inch. This is one of the most useful maps published in this country, 
and, because of its comparative accuracy, great detail, and small cost, 
its economic and scientific features should be known by all. It shows 
not only such topographic features as rivers, lakes, roads, railroads, 
villages, often separate houses, ferries, bridges, mines, quarries, etc., 
but by contour lines the absolute and relative elevation of any and 
all points of the area. 

The atlas sheets are valuable aids in the study of geography and 
geology. Some of the points which a student can frequently interpret 
from the contour map are : (1) The elevation of any and all points 
above sea level and hence of any point relative to any other. From 
one of these maps covering your home district it would be possible 
for you to tell how many feet your house is above or below the school- 
house. Try it. (2) The steepness of the hillsides. (3) The location 
of the cliffs. (4) The extent of the drainage basins. (5) The topo- 
graphic age, or place in the cycle of erosion, whether young, mature, 
or old. (6) The kind and structure of the rocks, whether igneous 
or stratified, whether folded or crumpled, or not. (On some areas 
this cannot be determined from the map.) (7) Whether river piracy 
has taken place or is taking place. (8) Frequently the character 
of the climate can be inferred, along with the probable industries 
carried on in the region, and the density of the population. 



PLATE I 




Pan of Wattins, N. Y., Sheet, U. S. Geological Survey. 



South End of Seneca Lake, One of the Finger Lakes of New 
Yobk. The Town of Watkins is Built on Portion of a Delta. 



THE EARTH AS A PLANET 33 

They are serviceable and interesting to travelers. One learns in 
time to select the best roads from the study of the map, or in a region 
where roads are absent, to choose the best route for travel from place 
to place. 

The contour maps are of great service in laying out routes for road- 
ways, railways, electric lines, aqueducts, pipe lines, and irrigating 
ditches. 

For these and other reasons contour maps should be thoroughly 
studied so that the student can properly interpret them. See Plates 
I, II, III, and IV. 

QUESTIONS 

1. Name the planets of the solar system in the order of size. 

2. How many satellites has each of the planets ? 

3. Which of the planets is an evening star now? Which a morn- 
ing star? 

4. Name all the sources of light, heat, and power that are used 
by man, and state how each is stored-up energy of the sun. 

5. How would the shape of the earth differ from that at present 
if it rotated more rapidly? If it rotated more slowly? 

6. What would be the length of our day if the earth rotated twice 
as fast as it does ? How long is a day on the planet Jupiter ? 

7. How much should you weigh on the moon? On Jupiter? 

8. If you could travel north on a straight line from the equator 
towards the north star, how far would you be from the north pole 
after going half the length of the polar diameter of the earth ? 

9. If the earth's axis were inclined 45° to that of the ecliptic in- 
stead of 23° 27', what effect would it have on the seasons in Chicago ? 

10. If winter in the northern hemisphere should come when the 
earth is at aphelion, what effect would it have on the seasons in the 
United States ? How do the seasons in Buenos Aires differ from those 
in New York? 

11. If a place is six miles west and eight miles south, how far is it 
in a direct line ? 

12. If a person at New Orleans should travel ten degrees west, 
and another person should travel ten degrees west from Duluth, which 
one would travel farther in miles ? 

13. Prove that the earth is not the shape of an egg or of a cube. 

14. What is the latitude of a place where the sun is 60° above the 
horizon at noon on June 21st? 



34 ELEMENTS OF PHYSICAL GEOGRAPHY 

15. What would be the altitude of the sun at noon on March 21st 
in 40° N. latitude? 

16. What time would it be in Denver when the sun is on the 
meridian at St. Louis? 

17. If you lived in the S. E. 1 of the S. E. 1 of Sec. 36, how far 
would you need to travel to visit a friend in the S. W. { of the N. W. J 
of Sec. 8 in the same township ? 

18. How far is it from the middle of See. 2 in T. 3 N., R. 4 W., to 
the S. E. i of the S. W. \ of Sec. 20 in T. 4 N., R. 2 E. ? 

19. How much longer (or shorter) is a lunar day than a solar day? 
than a sidereal day? 

20. At what hour in the morning of November 11, 1918, was the 
armistice signed ? At what hour did New York City receive the news ? 
At what hour did your town or city begin celebrating? 

21. If you had a compass at the north pole, which direction would 
the needle point? If you were at the south end of Greenland, which 
direction would it point ? 

22.. What are the advantages of a contour map? 

23. Why is not the sun always on the meridian when the clock 
strikes twelve? 

24. How does a planet differ from a star ? What is the shape of a 
star? 

25. By latitude and longitude find the place on the earth directly 
opposite you. 



CHAPTER II 
THE ATMOSPHERE 

The atmosphere is the gaseous portion of the earth which 
surrounds the liquid and solid portions. Floating in sus- 
pension in the atmosphere are large but variable quantities 
of moisture in the form of invisible vapor, and also condensed 
vapor in the form of clouds, fog, or mist, along with many 
dust particles and microscopic organisms. All this material 
while in the atmosphere may be considered a part of it in the 
same way that the portions of the gases which penetrate the 
water and the land may be considered as portions of the water 
and land spheres for the time. The air is as truly a part of 
the earth as the water or the land. It even approaches, possibly 
exceeds them in volume, although it is less in mass. 

The science which treats of the atmosphere, its position and 
functions, its phenomena and the laws governing them, is called 
meteorology. 

39. Functions of the Air.. — In the economy of the earth the 
air serves many important functions, such as (1) diffusing 
light; (2) conducting sound; (3) retaining heat; (4) sup- 
porting life in many ways ; (5) supporting combustion ; (6) mov- 
ing ships ; (7) driving windmills ; (8) reducing the weight of 
bodies submerged in it, thus making it possible for some animals 
to walk and others to fly ; (9) producing waves and ocean cur- 
rents; (10) moving sand and dust and wearing away rock; 
(11) distributing moisture and heat ; (12) furnishing a medium 
for flight by aeroplanes. What other functions can you name? 
Can you see the air? Can you feel it? 

35 



36 ELEMENTS OF PHYSICAL GEOGRAPHY 

40. Composition of the Atmosphere. — The atmosphere 
consists of a mixture of nitrogen and oxygen in the proportion 
of nearly four parts of nitrogen to one of oxygen, along with 
small but variable quantities of carbonic acid gas, water vapor, 
argon, crypton, helium, and probably other rare but yet un- 
known gases, besides variable quantities of dust particles. 

41. Nitrogen. — - Nitrogen, which forms about four-fifths of the 
bulk of the atmosphere, is one of the most inert of the gases. It 
has little or no tendency to combine with the other elements under 
normal conditions ; but with the aid of bacteria, certain plants, such 
as clover, have the power of secreting it in their roots in the form of 
nitrates which greatly enrich the soil. Nitrogen combined chemically 
with oxygen and water forms nitric acid. If this comes in contact 
with other substances, such as soda or potash, it combines with them, 
forming compounds called nitrates. Nitrogen combined chemically 
with hydrogen in the proportion of one to three forms ammonia gas 
(NH 3 ), which in combination with water forms aqua ammonia (NH 4 
HO). In the form of ammonia and nitrates, the nitrogen forms a 
plant food, and through the plant an animal food. 

42. Oxygen. — Oxygen forms about one-fifth of the atmosphere 
and is much more active and aggressive in its character than the 
nitrogen. It is the chief agent in combustion ; in fact nearly all 
burning consists of the chemical union of oxygen with carbon, form- 
ing carbon dioxide and other gases, whether it be in fires, where it 
produces heat and light, or in our own bodies, where it forms heat but 
not light. Oxygen is ever active also in combining with metals and 
minerals in the rocks of the earth. A knife left on the ground, in a 
few days is covered with rust ; in a few months it crumbles to frag- 
ments, " eaten up" by the rust ; in other words, by the oxygen of the 
atmosphere. Oxygen is also an important agent in the decomposition 
of dead animal and vegetable matter, thus helping to purify the air. 
This is accomplished largely by the aid of bacteria, which are also 
important aids in forming nitrates. In the form of ozone it is even 
more active. Oxygen forms half of the rocks of the earth's crust, and 
eight-ninths of the water. It is being taken from the atmosphere by 
animals, by fires, by the rusting of rocks and minerals. It is being re- 
turned by plants, which take the carbon dioxide gas from the air and 
separate it into the elements, carbon, which makes new compounds 
forming part of the plant, and oxygen, which is returned to the air. 



THE ATMOSPHERE 37 

43. Carbon Dioxide. — Carbon dioxide or carbonic acid gas 
(C0 2 ) forms a small but important part of the air. The proportion 
varies greatly at different places and times, but averages about 0.03 %. 

It is one of the chief heating agents in the atmosphere and thus 
has considerable influence on the climate, owing to a variation in the 
proportion present from time to time. It is a denser, heavier gas 
than nitrogen or oxygen, and absorbs and holds the heat from the sun's 
rays, thus serving as a blanket to warm the earth. It is directly 
necessary to plant life, furnishing the most important article of food 
for the plant, and it is indirectly necessary to animal life. Why? 
When dissolved in water it becomes an active agent of solution and 
disintegration in the rocks, especially the limestones. 

Carbonic acid is added to the atmosphere by the breath of animals, 
by the decay and combustion of all animal and vegetable matter, by 
volcanoes, by carbonated springs, and from the sea water. It is ex- 
tracted from the air by plants, which fix the carbon in their tissue and 
give the oxygen back to the air, and by the disintegration of rocks, 
in which it is combined with other materials to form carbonates ; and 
it is absorbed by the sea water and fresh waters where these are not 
already saturated with it. Owing to this circulation through the rocks 
and the sea, the proportion of. this gas in the air varies sufficiently 
from one geologic age to another, it is thought, to affect the climate 
materially. Such changes are too slow to be perceptible during one 
or two generations. 

44. Water Vapor. — Water vapor is a small, variable, but very 
important constituent of the air. The water in an invisible gaseous 
condition is absorbed by the atmosphere from the surface of the ocean, 
other bodies of water, and the moist land. The gases ejected from 
volcanoes also supply large quantities of vapor to the air. Another 
source of supply is in combustion, and as exhalation from the lungs of 
animals and from the leaves of plants. 

The water vapor is the source of clouds, fogs, rain, snow, hail, dew, 
and frost. It is the circulation of the water vapor in the air and its 
precipitation that makes life possible. Without it all land areas would 
be deserts. The distribution of water vapor by the air, and its pre- 
cipitation, not only support life on the land areas, but form the rivers 
and glaciers, which are the most active agents in carving the rock 
surfaces into beautiful landscapes and ultimately wearing down the 
mountains and plateaus. Water vapor is an important agent in the 
distribution of heat in the atmosphere. The heat required to vaporize 



38 ELEMENTS OF PHYSICAL GEOGRAPHY 

the water from the surface and carry it into the air, is set free when the 
vapor condenses as rain, snow, etc. The vapor also acts like carbonic 
acid and dust in changing the sun's insolation to heat, and radiating 
it in the air. 

45. Dust. — Another important constituent of the air is dust, 
which is everywhere present, but most abundant over the land areas 
near the surface in dry weather. Why? It consists of exceedingly 
fine particles of pulverized rock carried up by the air currents or blown 
out from volcanoes, of particles of unconsumed fuel in the smoke, of 
living germs in the form of bacteria and microbes, or of decayed plant 
and animal tissue. In a ray of sunshine passing through a small 
opening into a dark room, one can see a vast number of the dust 
particles, but there is a much larger number invisible because they are 
so very small. 

The dust of the air is thought to be an important aid in the pre- 
cipitation of moisture. The dust particle becomes a center of con- 
densation of moisture until there is sufficient to form the raindrop or 
the snowflake, which then falls to the earth. It acts with the car- 
bonic acid and the moisture in heating the air, as each little dust 
particle becomes a little furnace or reservoir of heat, which it radiates 
in all directions. It influences the color of the sky, the brilhant red 
sunset being due largely to the dust particles in the air. The bacterial 
portion aids decomposition and the spread of disease. 

Dust is sometimes classed as an impurity in the atmosphere, but 
since it is always present, and serves a useful if not a necessary purpose 
for the support of life, it is properly one of the constituents of the air. 

46. Pressure of the Air. — Because the pressure of the air 
is exerted equally in all directions, it long remained unper- 
ceived. If we should exhaust all the air from underneath a 
scale pan, we would find a weight of air on the pan of about 
fifteen pounds to the square inch or a little more than a ton 
to the square foot ; that is, provided the weight were taken at 
sea level ; with change of temperature or change of elevation 
the pressure changes. It increases below sea level and de- 
creases above sea level. It decreases with an increase in 
temperature and increases with a decrease in temperature, 
because the warm air expands and is therefore lighter than 



THE ATMOSPHERE 



39 



the same volume of cold air subject to the 
same pressure, as the cold air contracts and is 
hence heavier than a similar volume of warm 
air. 

Weight on the earth is the effect of gravity, 
which tends to draw all bodies toward the center 
of the earth ; hence the weight of the atmosphere 
at any point is its vertical pressure, but owing 
to its extreme mobility, this pressure, due to 
weight, is exerted equally in all directions. 
Hence, under ordinary conditions we do not find 
the scale pan pressed downward by air, because 
there is the same pressure underneath as on top. 
The pressure of ten tons or more on the outside 
of the human body is not felt because there is 
a corresponding pressure on the inside. The 
weight of a cubic foot of air at sea level at a 
temperature of 60° is 0.075 pound, while the 
pressure transmitted by this cubic foot is more 
than a ton on each side. 

47. Barometer. — The instrument commonly 
used in weighing the air, that is, in determining 
its pressure, is a barometer, which in its simplest 
form consists of a glass tube closed at one end, 
filled with mercury and inverted in a cup of the 
same metal. At sea level the mercury settles 
in the tube until the top of it is about 30 inches 
above the level of that in the cup. Now a 
column of mercury 30 inches high weighs 15 
pounds per square inch at the base of the 
column, hence the weight of the air pressing 
on the surface of the cup outside of the tube 
must be equal to 15 pounds per square inch, 
since the two balance each other. Why is mer- 



Fig. 17. — Mer- 
cury barometer. 



40 



ELEMENTS OF PHYSICAL GEOGRAPHY 



If water were used, 



cury used ? Why not some other liquid ? 
how long a tube would it require ? 

An aneroid barometer differs from a mercurial one in substituting 
for the column of mercury a small corrugated metallic box from which 
the air has been exhausted as nearly as pos- 
sible. The surface of this box is connected 
through a series of levers to a needle in such 
a way that when the sides of 
the box are pressed in, as 
would be the case with an 
increase of pressure in the 
air, the needle will turn 
around on a dial like the 
hands of a watch, and when 
the pressure decreases, the 
needle moves in the 
opposite direction. 
The dial of the 
aneroid is marked 
so that movements 
of the needle indi- 
cate the number of 
feet the barometer 
has been taken up 
or down, or it may 
be marked in inches 
to correspond to the 
movements of the mercury in the other barometer ; in fact it generally 
has both scales. Because it can be carried in the pocket like a watch 
it is much more convenient for determining altitudes than the bulky 
mercurial barometer. (See Fig. 18.) 

48. Density of Air. — When a mercurial barometer is carried 
up a mountain the mercury gradually falls in the tube, because 
of the decrease in the pressure of the atmosphere, until at an 
elevation of 3.4 miles above the sea there is only 15 inches in 
the tube ; that is, at that height the air would be only half as 
dense or heavy as at sea level. At greater elevations the density 
has been estimated as follows : 




Fig. 18. — Aneroid barometer. (Central Scientific Co.) 



THE ATMOSPHERE 41 

Elevation 6.8 miles, density }, and barometer reading 7.5 inches 
Elevation 10.2 miles, density f , and barometer reading 3.75 inches 
Elevation 13.6 miles, density ^, and barometer reading 1.87 inches 
Elevation 17.0 miles, density -fa, and barometer reading 0.95 inch 

This estimate is based on the assumption that the density 
decreases in the upper atmosphere at the same rate that it 
does in the lower atmosphere ; that is, a decrease of one-half 
for every 3.4 miles ascent. 

49. Height of the Atmosphere. — The atmosphere extends 
out into space indefinitely if its density continues to decrease 
as indicated above, but the outer portion must be so exceedingly 
rare that it would appear like empty space. Less than 100 
miles above the surface of the earth it would be so rare that its 
presence would be difficult to determine. The upper limit 
of the atmosphere is unknown, if there is any upper limit, but 
that it extends some miles above the earth is shown by the 
luminosity of meteors. In space free from all gases, meteors are 
dark bodies, but friction with the air at the high velocity at 
which they move, heats them so that they become luminous. 
Since these meteors have been seen as luminous bodies many 
miles above the earth, it is assumed that the atmosphere has 
sufficient density at such elevations to render them visible. 

The change in density with altitude is noticed by persons in as- 
cending high mountains or rising in an aeroplane. Some people suffer 
greatly on Pikes Peak, less than three miles high, others can breathe 
comfortably on Mt. McKinley, four miles high. A few people can 
live at even higher altitudes, but very few persons could retain con- 
sciousness any length of time at elevations above five miles. No one 
has yet ascended to altitudes greater than five or six miles. Even 
though a person could remain alive at such elevations, which he could 
by carrying an oxygen tank with him, the air is not dense enough to 
support a flying machine. 

50. Pressure Curve. — If the barometer readings are re- 
corded at any point for several days, it will be seen that there 



42 ELEMENTS OF PHYSICAL GEOGRAPHY 

is a considerable variation. If a barometer should be read at 
regular intervals of an hour or two hours for several days and 
the results plotted on cross-section paper, the result would be a 
pressure curve. This pressure curve is plotted automatically 




Fig. 19. — Barograph. (Central Scientific Co.) 

and more accurately by an instrument called a barograph. 
(See Fig. 19.) The curve made by the barograph is called 
a barogram (Fig. 20). 




Fig. 20. — A barogram or pressure curve made by a barograph during the 
passage of a cyclone. 

51. Barograph. — The barograph used by the United States 
Weather Bureau is based on the principle of the aneroid instead of the 
mercurial barometer. It consists of a corrugated iron box from which 



THE ATMOSPHERE 43 

the air lias been exhausted so that an. increase in the pressure of the 
air depresses the surface of the box and a decrease in the pressure 
causes a corresponding elevation in the surface produced by a spring 
inside the box. These movements of the surface are magnified by a 
series of compound levers to which is attached a pen so adjusted as to 
leave its trace on the roll of cross-ruled paper which is moved by clock- 
work. This shows conclusively that the pressure at any place at any 
one time is dependent on the condition of the weather. If the effect 
of the weather on the barometer is known, then the process may be 
reversed and the record of the barometer may be taken as the in- 
dication of weather conditions ; and if along with this, the regular 
movements of the atmosphere are considered, the weather conditions 
may often be foretold for some time ahead. 

52. Isobars. — In order to compare barometer readings 
from different localities to determine probable weather con- 
ditions, it is neeessary to make a correction for the differences 
in elevation of the places and another for the differences in the 
temperature. Tables have been made out for this purpose, 
so that having the reading of the barometer and the thermometer 
and knowing the elevation of the point above sea level, it is 
only necessary to turn to the tables to make the necessary ad- 
ditions or subtractions to reduce the readings from different 
places to a common plane, which by common consent is taken 
as sea level. The records that are given on the government 
weather maps are all the corrected sea-level readings at the 
temperature of 32° F. 

In order to bring out graphically the results obtained from 
barometric readings at many different stations, lines represent- 
ing variations in pressure of one-tenth of an inch are drawn 
through points having the same barometric pressure. Such 
lines are called isobars (meaning equal pressure), and are shown 
on the daily weather maps by continuous black lines. Com- 
pare carefully several daily isobaric charts or weather maps 
with each other and observe how the pressure varies from day 
to day. \ 

\ 



44 ELEMENTS OF PHYSICAL GEOGRAPHY 

53. Barometric Gradients. — On the daily weather map most 
of the isobars are more or less concentric around centers, some of which 
are marked high and some marked low, meaning high pressure and 
low pressure. The barometric gradient is the rate at which the air 
pressure changes from place to place and particularly between a high 
and the nearest low. It indicates the direction in which the atmosphere 
tends to move, namely, from the high to the low, and the steeper the 
gradient, that is, the greater the number of isobars, the more rapidly 
the air moves and hence the stronger the wind. Test this by com- 
paring current weather maps on a windy day and a calm one. 

54. Temperature and Heat. — Temperature is the measure 
of the heat energy of any body. The instrument used for 
recording the temperature is called a thermometer (heat measure). 
In the common house thermometer mercury rises and falls 
through a capillary tube, from expansion and contraction with 
increasing and decreasing temperature, and generally indicates 
increase and decrease of heat. However, many bodies are 
capable of absorbing or giving off considerable heat without 
any perceptible change of temperature. Thus when heat is 
applied to ice, the temperature does not vary until all the ice 
has been changed to water. The heat required to change a 
pound of ice to water at the same temperature would raise the 
pound of water from 32° to 174° F. This is called latent heat 
of fusion, and will be given off again before the water will freeze. 
It requires a large increment of heat to change water from a 
liquid at 212° to a vapor at the same temperature, the latent 
heat of vaporization. (This is technically expressed in heat 
units called calories. A calorie is the amount of heat required 
to raise a gram of water one degree Centigrade. The latent 
heat of vaporization of water is 536.6 calories.) 

55. Thermometer. — The temperature of the air is usually 
measured by a thermometer, which consists of a small bulb 
filled with metallic mercury, that is attached to a capillary 
tube in which the mercury rises when it is heated and in which 



THE ATMOSPHERE 



45 



it sinks when it is cooled. On the tube or on a flat surface 
to which the tube is attached, is a scale marked off in degrees, 
from which is read the number corresponding to the height of 
the mercury in the tube. 

The mercury thermometer may be used for measuring temperatures 
between —40° F., the freezing point of mercury, and 648° F., the 
boiling point. For lower temperatures some other liquid, as alcohol 
or ether, is used ; for higher temperatures some more resistant metal 
or metals, or some other device, is used. Describe a maximum and a 
minimum thermometer and the Fahrenheit, Centigrade, and abso- 
lute scales for grading thermometers, if these instruments are at hand. 

56. Temperature Curve. — The variation in temperature 
at any place from time to time may be represented by a tempera- 
ture curve, as shown in Fig. 21. The curve may be constructed 
for any period of time for which the thermometer readings 




Fig. 21. — A thermogram or temperature curve made by a thermograph.. 



have been taken. The thermograph automatically records 
such a curve with greater accuracy of detail than can be shown 
on one drawn from thermometer readings. Study curves of 
this kind if available, and note the time of day when the maxi- 
mum and minimum temperatures occur. Each student should 
plot a temperature curve for a week or a month, from data 
obtained by reading the thermometer and recording the tem- 
perature three or more times each day. 



46 



ELEMENTS OF PHYSICAL GEOGRAPHY 




A thermograph is an instrument for recording automatically the 
temperature for a fixed period of time in much the same way as a 

barograph records 
pressure. The 
record of the 
thermograph is 
a thermogram or a 
temperature curve. 
(See Fig. 22.) 

57. Sources of 
Heat. — The 

three sources of 
heat supply on 
the earth are (1) 
the sun, (2) the 
stars and other 
heavenly bodies, 
(3) the internal 
heat of the earth. In quantity the last two are insignificant 
when compared with that from the sun, which is the source of 
not only nearly all the heat, but the light, and other forms of 
energy as well. The radiant energy that comes from the sun 
is known as insolation ; this manifests itself on the earth in part 
as heat, in part as light, and probably in several other forms of 
energy. The earth receives about one two-billionth portion of 
the sun's insolation, and a large part of that received is not 
retained, but is reflected or radiated off into space. 

The heat generated in our stoves and furnaces by the combustion 
of fuel is the latent heat of the sun that has been stored up in the 
wood, coal, oil, gas, or other fuel. The heat obtained by electricity 
generated from water power is the heat energy from the sun that is 
stored up in the water evaporated from the sea. 

A small portion of the sun's rays as they pass through the atmos- 
phere, is intercepted by dust particles and heavier gases and changed 
to sensible heat, but the greater part passes directly through to the 



Fig. 22. — Thermograph. (Central Scientific Co.) 



THE ATMOSPHERE 



47 



^ r 



d 



surface of the earth, where a portion is absorbed by the rock-and-water 
surface and changed to latent or radiant heat, and a portion is reflected 
back into the atmosphere. The proportion of rays absorbed to those 
reflected, varies greatly with different surfaces. More are reflected 
from a water surface than from rock, and more from light-colored 
rocks than from dark-colored ones. There is likewise a wide variation 
depending on the angle of inclination of the rays to the surface. The 
greatest percentage of insolation is absorbed under the vertical rays ; 
as the rays vary from the vertical there is an increasing proportion 
reflected, until the tangent rays, such as those at sunrise and sunset, 
are nearly all either reflected or else pass directly through the at- 
mosphere into space beyond. 

58. Ways in Which the Air is Warmed. — The atmosphere 
is warmed (1) in direct insolation by the part that is changed 
to heat by contact with the denser constituents of the air, 
(2) by radiation, con- d 

duction, and convec- 
tion from the insola- 
tion that is changed 
to heat in the atmos- 
phere and on the sur- 
face of the earth. 
Waves of heat energy 
radiate out in all di- 
rections from the sur- 
f a ce of all warm 
bodies. It is the radiated heat we feel when standing by the 
fire. If, however, we place the end of a poker in the fire, after 
a time the end in the hand becomes warm by the heat conducted 
through the iron of the poker. The air warmed by radiation 
expands and rises above the cooler, denser air ; this replaces the 
warmer air, thus starting convection currents which assist 
radiation and conduction in distributing the heat (Fig. 23). 
Air is also warmed (3) by compression. When air is pumped 
into ah automobile tube, part of the energy used in working the 



b b 










J 



Fig. 23. — Convection currents. 



48 ELEMENTS OF PHYSICAL GEOGRAPHY 

pump is changed to heat in the compressed air. The light air 
from the Rocky Mountains is forced down by air currents into 
the denser air on the plains, where it is warmed by the greater 
pressure and forms the warm chinook winds. Air, finally, is 
warmed (4) by the precipitation of rain or snow. The heat 
required in vaporizing water is given off in the air when the 
moisture is condensed in rain, snow, or hail. When water 
freezes, the latent heat of fusion is returned to the air ; that is, 
heat required to melt the ice without any sensible change of 
temperature is returned to the air when water changes to ice. 
(See Sec. 54.) 

The heating of air by compression and the cooling by expansion is 
known as adiabatic heating and cooling. 

59. The Hottest Part of the Day. — The atmosphere and the 
earth- underneath it receive heat directly frorn the sun during the 
day, receiving the greatest quantity at midday, when the rays are 
most nearly vertical. The temperature, however, is the highest from 
one to two hours after noon. Why? There is a more or less regular 
decrease in the heat received from the sun as one goes from the tropics 
towards the poles. Why ? 

60. Effect of Latitude. — The seasonal changes are most 
marked at and near the poles, and least at and near the equator, 
owing to the fact of less variation in the inclination of the sun's 
rays in the tropics and of greater uniformity in the distribution 
of sunlight and darkness. 

The temperature decreases with an increase of latitude at 
the average rate of about 1° F. for 1 degree, or about 70 miles, 
of latitude. 

61. Effect of Altitude. — The temperature decreases with 
altitude at the average rate of about 1° F. for every 300 feet 
of ascent ; heuce, at the equator one would find about the 
same change in temperature by ascending a mountain six miles 
high as in going to the north or south pole. The reason for 
the rapid decrease in temperature in ascending the mountain 



THE ATMOSPHERE 49 

is that the air is less dense, and contains less carbon dioxide, 
water vapor, and dust particles, which serve to retain the heat 
at lower altitudes. 

While the maximum heat is received at noon under the vertical 
rays of the sun, the gradation from the vertical noon rays to the 
tangent rays of morning and evening and from the tropics to the poles 
is not uniform. Among the many factors causing local variation in 
temperature of the air, are water, clouds, winds, pressure, and topog- 
raphy. 

62. Effect of Water. — Bodies of water tend to equalize the 
temperature of the region bordering them, because they absorb 
the heat less rapidly than the land, do not become so hot during 
the day or during the summer season, and, since they part with 
their heat less rapidly than the land, do not cool so quickly; 
hence the water is^cooler than the land in the summer and 
warmer in the winter, and exercises a corresponding effect on 
the atmosphere that comes in contact with it. Therefore 
points along the seacoast have a more uniform climate than 
inland points. The same thing is true in a less degree of the 
lakes, especially the larger ones. Even the Finger Lakes of 
central New York temper the climate on their shores, but their 
influence does not extend so far away as is the case with larger 
bodies of water. 

The chief reasons for the tempering influence of the water on the 
air are : (1) greater specific heat of water; (2) greater mobility of 
water, as by means of currents the heat is rapidly and widely distrib- 
uted ; (3) evaporation, in which the heat becomes latent and does not 
affect the temperature ; (4) checking the radiation by clouds and fogs, 
which are more prevalent over water areas ; (5) absorption of latent 
heat in melting ice ; (6) return of latent heat of fusion when water 
changes to ice. 

63. Effect of Clouds. — Clouds retard loss of heat by radia- 
tion. In the spring and autumn, when the temperature is 
near the freezing point, one frequently hears the remark, " If 



50 ELEMENTS OF PHYSICAL GEOGRAPHY 

it clears off tonight there will be a frost." On a clear night 
the heat received from the sun during the day is rapidly radiated 
out into space. If the clouds are present this radiation is 
checked in a large degree, because they do not permit the heat 
to pass through as readily as it passes through clear atmosphere, 
and they also radiate and reflect heat back to the earth. 

64. Prevailing Winds. — The prevailing winds affect the 
temperature in some places. In India, for about half the year, 
the winds blow from the Indian Ocean warm and moist. Dur- 
ing the other half, they come from the Thibetan Plateau and 
Himalaya Mountains dry and cold. 

65. Effect of Pressure. — In areas of high pressure, the air is 
being warmed because it is under pressure, and in areas of low pressure, 
it is being cooled because it is rising and expanding. However, the 
temperature of the air near the earth is higher in the low pressure 
areas than in the high ; in fact, that is the reason why it is low, because 
the temperature is higher and hence the air is lighter and is crowded 
up by the inward pressure of the surrounding heavier air ; the tempera- 
ture is kept high because the air moves into the center along the surface 
of the earth, where it is warmed by conduction and frequently by 
precipitation of the moisture ; it cools by expansion as it rises, but is 
then beyond the reach of our senses. The air is cooler and feels cooler 
in the high centers because it is descending from the higher altitudes, 
where it is much colder. The clear air of the high center favors 
radiation of heat and in that way lowers the temperature. Cold 
waves come from the high centers in the winter. The fact that the 
air is warmed in the high and cooled in the low is shown in two ways, 
by comparing the temperature taken at high altitudes, by means of a 
kite or a balloon, and second by noting that in the highs the air is 
clear and generally free from clouds and rain, while in the lows, it is 
cloudy and frequently precipitates rain or snow. Cooling the air 
condenses the moisture, and warming it increases its capacity for 
moisture, causing it to dissolve the clouds instead of condensing them. 
(See Sec. 86.) 

66. Influence of Topography. — In high latitudes, where 
the sun's rays are quite slanting even at midday, there is a 
great difference in the quantity of heat received on the warm 



THE ATMOSPHERE 



51 



south slopes, which may be at nearly right angles to the noon- 
day sun, from that on the cool north slopes, where the rays may 
be nearly tangent or in some cases never strike even at noon- 
day. Slopes facing west or southwest are warmer than those 




Fig. 24. — Diagram illustrating the effects of sunshine on the opposite sides 
of an east-west valley. The north side receives the nearly vertical rays of the 
sun, while the south side is in the shadow. In cold weather this causes more 
frequent thawing and freezing and hence more rapid weathering on the north 
side, and in the spring it produces earlier vegetation. 



facing east or southeast. The difference may be manifest 
in a region moderately hilly, but it is still more pronounced 
in a mountainous country, especially so where the mountains 
extend east and west. Are there any spots in your vicinity 
where the spring flowers bloom first? Where the early fruits 
first ripen? What is the relation of such spots to the sunshine ? 
(See Fig. 24.) 

67. Isotherms. — The thermometer is read and recorded 
twice daily, at eight o'clock morning and evening, at a great 
many stations in the United States and Canada, and the results 
distributed by telegraph to certain places, where they are re- 
corded on maps ; lines are drawn connecting points which have 
the same temperature : such lines are called isotherms, meaning 
equal temperatures. By consulting a number of daily weather 
maps for successive days, it will be seen that there is con- 
siderable variation in the position of the isotherms from day 



52 ELEMENTS OF PHYSICAL GEOGRAPHY 

to day. These may all be averaged and a map constructed 
showing the mean for a month, a season, or a year. (See 
Fig. 25 ; note the variations on the land and on the sea on the 
different charts.) 

68. Temperature Gradient. — On some of the weather maps 
there are more isotherms than on others, showing at times a much 
greater difference or range of temperature. In general, great dif- 
ferences in temperature are found associated with great differences 
in pressure ; in fact, extremes of temperature cause extremes of 
pressure. The rate of change between the high and low temperatures 
is called a temperature gradient, and the gradient is higher where the 
isotherms are more numerous and closer together. Steep temperature 
gradients are associated with steep or decided pressure gradients. 
(Compare Figs. 28 and 40, and note that high pressure is associated 
with low temperature and vice versa. The gradients are high in each 
case:) 

69. Temperature Zones. — In the isothermal chart of the 
world, it is shown that the isotherms of 70 degrees lie schne 
distance on each side of the equator, but at different distances 
in the January and the July charts. These isotherms inclose the 
warm or hot zone, through the midst of which runs a line of 
highest temperature, the heat equator, which lies north of the 
true equator in July and south of it in January ; that is, it 
shifts north and south following the sun. The temperature 
belt inclosed between isotherms of 70 degrees and 30 degrees 
is called the temperate zone, while the region around the 
poles outside of the thirty degree isotherm has a frigid tem- 
perature. All of these zones it will be observed shift north 
and south following the movements of the heat equator. 
(Study Fig. 26.) 

All of the temperate zones are" more nearly uniform in the southern 
hemisphere than in the northern, and more uniform on the southern 
oceans than on the southern continents. Why? The student should 
be able to state the reasons from the data in the preceding pages. 




Fig. 25. — Isothermal chart for January, for July, and for the year. 

53 



54 ELEMENTS OF PHYSICAL GEOGRAPHY 

MOVEMENTS OF THE ATMOSPHERE 

70. Winds. — When a fire is kindled, the air in and over the 
fire rises, as we can see from the smoke which moves with it. 
It rises because when heated it expands and the pressure of 
the cooler and hence denser air around the fire pushes it up. 
If the fire is a small one the movement of the air towards the 
fire is scarcely perceptible, but in a large fire the movement is 
quite perceptible and is called wind. It is part of the convection 
current started by the fire. (See Fig. 23.) 

Any portion of the earth's surface that is heated more than 
adjoining portions, warms and hence expands the atmosphere 
in contact with it ; the surrounding cooler air crowds the heated 
air up, thus starting a convection current similar to that started 
by the fire. The bottom of the convection current, where the 
movement is more or less parallel with the surface of the earth, 
is called wind. 

Differences in temperature in the air cause differences in pressure, 
which in turn produce movements or currents of air, and the lower- 
more or less horizontal movements are called winds. The ascend- 
ing and descending currents are called calms. In the areas of rising 
air the pressure is low, in the descending currents the pressure is high. 
The winds blow from areas of high pressure to areas of low pressure 
with a velocity increasing with increase of barometric gradient. (See 
Sec. 53.) 

The wind is named from the point of the compass from which it is 
blowing. Thus a west wind means an air current from the west. 
The winds may be grouped into three general classes, (1) terrestrial 
or planetary, (2) cyclonic or eddying, and (3) land or continental. 

TERRESTRIAL OR PLANETARY WINDS 

71. Doldrums. — Winds due to the condition of a rotating 
planet heated by the sun, occur on all planets that have an 
atmosphere and are called terrestrial or planetary winds. An 
excessive heating in the region of the equator, causes the air 
to expand and flow off aloft, thus producing a low pressure 



THE ATMOSPHERE 



55 




Fig. 26. — Climatic zone map based on isotherms. Compare with Fig. 25 
and note how the zones shift with the seasons. 



56 ELEMENTS OF PHYSICAL GEOGRAPHY 

belt of calms known as the doldrums or the equatorial calms, 
and a high pressure near the tropics known as the horse 
latitudes or tropical calms, formed by the descending air. 
(See Fig. 27.) 

72. Trade Winds. — The warm air in the doldrums is forced 
upwards by the air which crowds in from the trade winds on 
both sides. The trade winds do not move directly north and 
south to the equator, but are deflected to the west because of 
the rotation of the earth, which according to Ferrel's law (See 
below) causes a deflection of all winds, cyclonic as well as 
terrestrial, to the right of the barometric gradient in the north- 
ern hemisphere and to the left in the southern hemisphere. It 
is because of the regularity with which these winds blow over 
the ocean that they are called trade winds. While they are 
still important factors in commerce, they were much more so 
when all the vessels were sailing vessels, before the days of 
steam navigation. 

/~ The trade wind belts are much less regular over land areas than 
/ over sea areas, owing to differences in temperature between land and 
^-water areas, and between land areas at different elevations. 

Since the doldrum belt shifts north and south following the sun 
during the change of seasons, the trade winds and other belts shift 
with it. 

Ferrel's Law. — Ferrel's law of wind movement is that_all 
winds are deflected to the right in the northern hemisphere and to the 
left in the southern hemisphere. This is because the rotation of the 
earth gives the surface the greatest velocity at the equator. Thus 
winds blowing from the tropics towards the equator are deflected 
westward and become northeast winds in the northern hemisphere and 
southeast winds in the southern ; and winds moving north from the 
Tropic of Cancer are deflected to the right 'eastward) and become 
southwesterly winds, while those moving sou b from the Tropic of 
Capricorn are deflected to the left (eastward) and become north- 
westerly winds. 

73. Tropical Calms. — The antitrades are caused by the ascending 
air at the equator overflowing toward the poles in the higher atmos- 



THE ATMOSPHERE 



57 



phere, above the trade winds and in an opposite direction. In the 
vicinity of the tropics, the antitrades descend in part to the surface, 
but since the descent is vertical or nearly so, they form belts of 
calms known as the horse latitudes or tropical calms. 




Winds and Rains of July — Northern Summoi. 



Fig. 27. — Planetary wind and rain belts in summer and in winter. The heat 
equator lies in the midst of the doldrums or equatorial rain belt. The tropical 
calm belts are not continuous on the larger land areas. 



68 ELEMENTS OF PHYSICAL GEOGRAPHY 

74. The Prevailing Westerlies. — The winds blowing from 
the horse latitudes toward the poles, like the trade winds and 
all other atmospheric movements, follow Ferrel's law and are 
deflected to the right in the northern hemisphere and to the 
left in the southern hemisphere, thus becoming northwest winds 
in the southern hemisphere and southwest winds in the northern. 
They are much less regular in their movement than the trade 
winds, frequently shifting direction to take part in the great 
spiral whirls known as cyclones and anticyclones. They are 
also subject to many local disturbances, such as land and sea 
breezes and the mountain and valley breezes. Beyond the 
belt of the prevailing westerlies, the movements of the at- 
mosphere are not so well known; the winds are thought to 
circle around the poles, forming the circumpolar whirl or eddy. 



CYCLONIC WINDS 

75. Cyclones. — A second class of winds, more local and 
variable than the terrestrial ones, are the cyclones, in which 
the winds move inward and upward in a spiral whirl or eddy 
around a region of low barometric pressure. In temperate 
climates, cyclones occur in the belt of the prevailing westerlies, 
where they cover large areas, sometimes 1000 miles or more 
in diameter. 

There are two movements of the air in a cyclone, a horizontal 
one towards the center and a vertical one at and near the center. 
The origin of the movement is probably due to the increase in 
temperature at the center, which causes the air to expand and 
overflow in the upper atmosphere, producing a downward 
pressure on the surrounding area. The crowding towards the 
center by this downward pressure pushes the expanded air up, 
and the movement is continued until equilibrium is again 
restored. The area is variously designated a cyclone, a low 
pressure area, or a low. It should be noted that the violent 



THE ATMOSPHERE 



59 



whirling storms which prove so destructive to life and property, 
called cyclones in the newspapers, are properly called tornadoes 
(described in Sec. 77). One or more cyclones pass across the 
United States nearly every week (Figs. 28 and 40). 




Fig. 28. — Weather map of United States showing a cyclone in February, 
1902, which caused excessive floods in the Ohio Valley. Continuous curved 
lines, isobars ; dotted lines, isotherms. The line of arrows shows path of the 
storm center from the Pacific coast. (U. S. Weather Bureau.) 

An anticyclone is an area of high pressure, or a high, where the 
air is descending and the winds blow out along the surface from 
the center. As the name indicates it is the opposite of a cyclone, 
the winds blowing from the anticyclone, or high, to the low. 
The higher or steeper the pressure gradient, that is, the greater 
the difference between the pressure in the centers of the low 
and the high, the stronger will be the winds. The air flows 
down the pressure slope at a rate proportional to the steepness 
of the slope. 



60 



ELEMENTS OF PHYSICAL GEOGRAPHY 



The weather in the United States is in a large measure determined 
by the highs and lows which move across the country in the general 
direction of the prevailing winds. (See Sec. 98.) 




Fig. 29. — Mean tracks of cyclones (lows) and anticyclones (highs) across 
the United States, and average daily movement of the same. (U. S. Weather 
Bureau.) 

Movements of Cyclones in the United States. — Cyclones some- 
times enter the United States from the northwest into Montana or 
the Dakotas and travel southeast to near the middle of the Mississippi 
Valley, and then northeast to, and sometimes across, the Atlantic 
Ocean. Sometimes they develop in the southwest, in New Mexico 
and Texas, and then move northeast off the continent. Sometimes 
they come in from the Pacific Coast. Sometimes they enter the north- 
ern and northeastern United States from the Hudson Bay region. 
Sometimes they pass out of the United States in the southeast. The 
rate of advance differs somewhat, but is generally faster in the winter, 
averaging about 800 miles per day, and slower in the summer, about 
500 miles per day. (See Fig. 29.) Test this by actual measurement 
from a series of weather maps for successive days. 

76. Hurricanes. — The tropical cyclones or hurricanes are 
great whirling storms from 100 to 300 miles in diameter, in 



THE ATMOSPHERE 



61 



which the winds frequently become very violent and destructive 
near the center. In the very center, however, the winds die 
away, leaving a calm with a clear sky, known as the " eye of 
the storm," which is said to vary from 10 to 20 miles in diameter, 
while immediately around it the winds are most violent, de- 




Fig. 30. — Map showing track of the Galveston hurricane in 1900. 
mate the rate of movement. (U. S. Weather Bureau.) 



Esti- 



creasing in intensity further from the center. The hurricanes 
originate on the oceans or oceanic islands within the tropics. 
The South Atlantic Ocean, however, appears to be free from 
them. In the North Atlantic they start near the West Indies 
and are known as West India hurricanes. They generally 
move in a northwesterly direction to the coast of North Carolina 
and thence northeasterly across the Atlantic Ocean, occasionally 



62 ELEMENTS OF PHYSICAL GEOGRAPHY 

reaching the coast of Europe before they are dissipated. Some- 
times they move up the east coast of the United States, causing 
great destruction to shipping. Occasionally one of the hur- 
ricanes passes into the Gulf of Mexico and thence into the 
Gulf States. It was one of these tropical hurricanes that 
passed over the city of Galveston in the year 1900 and de- 
stroyed the greater part of that city, besides doing much 
damage in the country farther north (Fig. 30) . Similar storms 
in the Pacific Ocean are called typhoons and often prove very 
destructive in the region of the Philippines and Japan. 

77. Tornadoes. — Cyclonic whirlwinds of small area and 
great intensity, that originate in the region of the prevailing 




Fig. 31. — View in path of a tornado, near Syracuse, N. Y. (Photo by 
the author.) 

westerlies, are called tornadoes. They are associated with 
thunder storms in the summer season and are most common 
on the plains of the west and south. It is not often that a 
violent tornado occurs east of the Allegheny Mountains, yet 
it does sometimes. (Fig. 31.) 



THE ATMOSPHERE 63 

They are generally marked by a funnel-shaped cloud suspended 
from the black mass of the thunder cloud. The storm generally 
moves east or northeast at a rate varying from 20 to 40 miles an hour, 
but the rotary velocity of the wind in the whirl may reach 500 miles 
or more. It is the most violent class of storms known in the United 
States, and some of the effects produced are almost incredible, such, 
for instance, as plucking the feathers from a chicken, tearing the tires 
from a wagon, tearing the laths from a house and driving them through 
the roof of a barn. 

When a tornado occurs on a lake or the ocean, a column of water is 
often formed in the vortex, and the tornado is then called a water- 
spout. A vessel caught in one of these waterspouts is liable to severe 
injury if not total destruction. It is thought that the water in the 
waterspout is mostly condensed from the clouds rather than drawn 
up from the sea. 

78. Hot Waves. — The warm south winds moving north- 
ward into a low pressure area, when unseasonably warm and 
dry, are called siroccos. The typical siroccos occur in Italy 
and are caused by the hot, scorching winds of the African 
desert flowing towards a low pressure area in central Europe. 
Similar but not such strongly marked siroccos occur at times 
in the Mississippi Valley, where they are known as hot waves, 
and cause drouth in the summer season and thaws in the winter. 
In Australia such winds are known as brickfielders. 

79. Chinook. — The chinook is the warm drying wind that 
descends the eastern slope of the western mountains to the 
Great Plains. The moisture has been precipitated on the west 
slope and summit of the mountains, and the wind then descends 
on the plains as a dry, hot wind. 

A snowfall on the Great Plains disappears almost like magic when 
the chinook wind comes. The frequency of these winds makes graz- 
ing possible on the plains in the winter season, as they remove the 
snow so that the stock gets access to the grass. Occasionally the ab- 
sence of the chinook wind for a week or more causes enormous loss of 
sheep, cattle, and horses on the plains. This loss is increased if during 
the interval there comes one of the dreaded western blizzards, which 
is a cold high wind accompanied by drifting snow. 



64 ELEMENTS OF PHYSICAL GEOGRAPHY 

80. Cold Waves. — A cold wave signifies a sudden fall of 
the thermometer, with a temperature extremely low for the 
season in any given locality. For the winter season in central 
New York a cold wave is defined as a 24-hour temperature 
fall of 20 degrees or more to a minimum of 10 degrees or lower, 
while in the warmest portions of the United States a drop of 
16 degrees to a minimum of 32 degrees is called a cold wave. 
It follows a cyclone, precedes an anticyclone, and is produced 
by the cold winds from the plains of the west and northwest 
moving east towards a low pressure. It is commonly char- 
acterized by fair weather, but occasionally it is accompanied 
by high winds and fine drifting snow, forming the much dreaded 
blizzard of the western plains. The norther of Texas, the bur an 
of Siberia, and the northeaster of western Europe are local 
names for a cold wave in the different countries. The last is 
produced when a low pressure swings a little farther south 
than usual and the cold winds move down from the plains of 
northern Europe. The much dreaded northeaster of the At- 
lantic coast of the United States is frequently the border of an 
advancing hurricane from the south, which means danger to 
vessels along the coast. 

CONTINENTAL WINDS 

81. Continental Winds. — A third class of winds, caused by 
local differences in the rate of radiation and absorption over 
land and water areas, is called continental winds, the most 
marked of which is the monsoon. 

82. Monsoons. — The monsoons are best developed in 
India, where the sea breeze in summer is so strong as to reverse 
the northern trade winds and cause the southeast trades to 
continue across the equator and over India as southwest winds. 
In the passage across the tropical seas, the air is heavily charged 
with moisture, which is precipitated on the south slopes of the 
Himalayas, producing an enormously heavy rainfall, in places 



THE ATMOSPHERE 



65 



as high as 35 feet per year. In the winter the winds are re- 
versed, and the cold winds from the plateau of central Asia 
blow across India to the sea. The winds, warming as they 
descend the mountains, blow across India as dry winds, taking 




Fig. 32. — Monsoon winds of India. Summer monsoons on the right ; 
winter monsoons on the left. 



up instead of precipitating moisture, and when they are pro- 
longed they produce drouth and famine in the land. The 
monsoons are caused by unequal heating of land and water, the 
land being warmer than the water in summer and cooler in^J 
winter (Fig. 32). 

83. Land and Sea Breezes. — The daily changes of temperature 
between land and sea are similar but less pronounced than the seasonal. 
The land is heated more during the day, causing the air to expand; 
the inflow from the sea produces the sea breeze, which blows during 
the middle of the day but dies out in the night. At night the land 
cools more rapidly and the wind is reversed to the land breeze, blowing 
from the land to the sea in the early morning. This reversal of the 
winds is utilized by fishermen, who sail out on the land breeze in the 
early morning and return on the sea breeze in the evening. 

84. Mountain and Valley Breezes. — The mountain radiates 
heat more rapidly at night than the valley, hence the cool air flows 
down the mountain and down the valley, forming the mountain breezes. 
In the daytime the reverse takes place, when the valley breeze blows 
up the valley and up the mountain. The mountain breezes are 
generally stronger than the valley breezes, because in blowing down 
the slopes they are aided by gravity. 



66 ELEMENTS OF PHYSICAL GEOGRAPHY 

85. Wind Velocity. — The velocity of the wind is recorded 
by an anemometer (anemos, wind ; meter, measure) . The 
style used by the Weather Bureau is shown by the accompany- 
ing figure. The wind blowing into the cups causes them to 




Fig. 33. — Anemometer or wind gauge. The wind blowing in the cups 
causes the rotation of a rod in the vertical shaft, which is connected by a series 
of cogwheels with a dial on which is recorded the movement of the wind. 
(Central Scientific Co.) 

revolve about the vertical axis, the rate of movement being 
indicated in miles per hour by an index at the base of the 
standard. 

The winds are roughly classified according to velocity as follows : 

(1) Calm signifies no movement or less than one mile per hour. 

(2) Light wind, less than 10 miles per hour, moves leaves on trees. 



THE ATMOSPHERE 67 

(3) Moderate, 10 to 15 miles per hour, moves small branches. 

(4) Brisk, 15 to 25 miles per hour, sways branches, raises dust. 

(5) High wind, 25 to 40, sways trees. 

(6) Gale, 40 to 60, breaks branches, uproots trees. 

(7) Hurricane or tornado, above 60, sometimes 500 miles per hour, 
destroys houses, etc. 

The direction of the wind is indicated by a wind vane, which con- 
sists of an arrow with two broad divergent flanges on the opposite 
end, free to rotate on a vertical axis. The arrow points in the direction 
from which the wind is blowing. The arrows on the weather maps, 
however, point the direction in which the wind is blowing. 



HUMIDITY AND PRECIPITATION 

86. Absolute and Relative Humidity. — The atmosphere 
always carries some moisture in the form of invisible water 
vapor, which is obtained by evaporation on contact with the 
surface of the ocean and the moist land. The amount of 
moisture in the atmosphere varies at different places, and at 
the same place at different times. The quantity of water in a 
given volume of air at any time, expressed in grains per cubic 
foot, denotes its absolute humidity. The amount of vapor 
present in the air, compared with what might be present if the 
air were saturated with moisture, gives the relative humidity 
and is expressed in per cent. If the air were perfectly free 
from moisture, which it never is, the relative humidity would 
be zero ; when it is saturated, the relative humidity is 100 per 
cent. 

While the absolute humidity may remain constant, the relative 
humidity varies with the temperature. The capacity of the air for 
moisture increases with an increase in temperature. Thus the air 
may be saturated, the relative humidity 100 per cent, at one tempera- 
ture, say 60 degrees ; if the temperature be raised to 80 degrees, the 
relative humidity would fall considerably below 100. On the other 
hand, should the temperature be lowered when the relative humidity 
is 100, precipitation would take place, that is, rain or snow would fall. 
When you hear the expressions, "The air is raw," "It is penetrating," 



68 



ELEMENTS OF PHYSICAL GEOGRAPHY 



what can you infer concerning the humidity? Why does cold moist 
air feel colder, and warm moist air feel warmer, than dry air at the 
same temperatures? 

87. Dew Point. — The temperature at the point of satura- 
tion is known as the dew point, and may be determined ex- 
perimentally by placing some ice in a cup of water and stirring 
it with a thermometer until moisture begins to form on the 
outside of the cup. The reading of the thermometer at that 
time will be the dew point of the atmosphere at that instant. 
By trying this experiment at several different times, it may be 
noticed that it varies considerably in air 
even at the same temperature. 

88. Hygrometric Instruments. — There 
are several different instruments used for 
measuring the humidity of the air. The 
essential part of a common hygrometer 
consists of a human hair deprived of its 
oil, which changes in length with a change 
in the percentage of moisture in the air. 
It is called the hair hygrometer. 

The sling hygrometer consists of two standard 
thermometers attached to a board, one of which 
has the bulb covered with wet muslin. They are 
whirled through the air for a short time to hasten 
the evaporation from the muslin. If the air is 
saturated with moisture, the two thermometers 
will read the same, but if the relative humidity 
is low, there will be rapid evaporation from the 
muslin covering the wet bulb, causing the mer- 
cury to fall. The difference between the wet and 
dry bulb readings increases as the relative hu- 
midity decreases. (Fig. 34.) 

A hygrodeik is a form of hygrometer in which 
the result is shown directly by adjusting two 
sliding pieces to the height of the mercury in the wet and the dry 
bulb thermometers, in such a way that they control the position of an 




Fig. 34.— Hy- 
grometer or sling psy- 
chrometer. A wet 
and dry bulb ther- 
mometer used for de- 
termining relative 
humidity. (Central 
Scientific Co.) 



THE ATMOSPHERE 69 

index which points out the number indicating the relative humidity 
in per cent. 

89. Dew and Frost. — When rapid radiation from objects 
on the surface of the earth causes the temperature of the air 
in contact to be lowered to the point of saturation, the moisture 
begins to condense, the point of saturation being commonly 
known as the dew point. Dew is formed on a clear night by 
the rapid radiation of the heat from the surface after the sun 
goes down. The air coming in contact with the cooled and 
cooling surface, is chilled by conduction, when some of the 
moisture condenses as dew; or, if below 32° F., it condenses in 
the crystal form as hoar frost. Dew or frost is formed most 
rapidly on the surface of substances which are the best radiators 
of heat, such as stone, grass, and leaves. 

Less dew is formed on a cloudy than on a clear night be- 
cause the clouds check radiation and prevent the surface from 
being sufficiently cooled. Dew is not formed on a windy night, 
because the air does not remain long enough in contact with 
the cool surface to be lowered to the dew point. Dew and 
frost do not fall. 

90. Clouds. — The condensation of the moisture in the air 
produces clouds of many different shapes and sizes. A cloud 
at the surface of the earth is called fog, or, if very light, mist. 
In the fog or cloud the moisture has been sufficiently condensed 
to form small particles large enough to intercept the rays of 
light. 

91. Classification of Clouds. — The more common forms of 
clouds are : 

(1) The cumulus, which often resembles great masses of 
snowy wool or cotton. It commonly has a flat or nearly 
regular base, but a very irregular and changing top, and is 
among the most common cloud forms in the summer season. 
It is formed by the ascending currents of warm air from the 



70 ELEMENTS OF PHYSICAL GEOGRAPHY 

heated land surface. The base is generally half a mile to a mile 
above the surface of the earth (Fig. 35). 

(2) The cirrus cloud is a feathery, plume-like form that occurs 
at a height of five to ten miles above the surface, and often 
consists of fine ice or snow crystals, owing to its great height. 
It forms in front of an advancing cyclone or low pressure area, 




Fig. 35. — Cumulus cloud. Common summer cloud. Frequently precedes 
a thunderstorm. 

and, moving ahead with the " low," is a pretty good indication 
of the advance of the storm center. It has been called a 
" weather-breeder " because it is frequently followed by rain 
or snow (Fig. 36) . 

(3) Stratus clouds occur in layers or strata near the surface, 
and frequently accompany rainstorms. They sometimes fall 
to the surface and form fogs. They are common in the early 
morning, but may occur at other hours. 

(4) Nimbus is a rain cloud, consisting of a dark gray to 
black mass, which generally covers the whole sky and from 
which the rain falls. (The term nimbus refers to a condition 
rather than to a form of cloud, and is usually understood to be 
any mass of cloud from which rain or snow is falling.) Any of 



THE ATMOSPHERE 



71 




Fig. 36. — Plumed cirrus cloud. (Photo by E. E. Howell.) 



72 



ELEMENTS OF PHYSICAL GEOGRAPHY 



the other clouds, especially the stratus or cumulus, may rapidly 
change to a nimbus. This is the most common cloud in central 
New York State during the winter, lasting at times for several 
days or even weeks, with the rain falling at intervals. 




Fig. 37. — Cirro-cumulus cloud. (Photo by E. E. Howell.) 

The different cloud forms mentioned may form many combinations, 

as cirro-cumulus (Fig. 37), cirro-stratus, cumulo-stratus, strato-cumulus 
(Fig. 38). 

92. Precipitation. — Rain occurs when the moisture con- 
denses into drops which fall to the earth. If the condensation 
takes place at temperature below 32° F. it forms snow, which 
bears the same relation to the rain in the clouds that frost does 
to dew on the surface of the earth. The moisture may con- 
dense as snow in the higher air and, in falling through warmer 
currents near the surface, may melt and reach the surface as 
rain. But if the rain should freeze while falling through the 
lower air it would form not snow but sleet. Sleet may also 
be half -melted snow. 



THE ATMOSPHERE 73 

Hail is thought to be a mixture of snow and frozen rain. It 
is formed during thunderstorms in the summer season, probably 
by the passage of the descending moisture through several 
air currents with temperatures alternately above and below 
freezing point. Hail storms, coming as they do in the summer 
season, often cause great damage to vegetation. 




Fig. 38. — Strato-cumiilus cloud as seen from above at sunrise on 
Pikes Peak. (Photo by Jackson.) 

93. Quantity of Rain. — The amount of rainfall is determined 
by measuring the depth of water in a vessel known as a rain 
gauge. Snow and hail are melted and the result given in the 
amount of water as though it had fallen as rain. It takes 
about eight or ten inches of snow to equal an inch of rain, but 
this differs with the kind of snow. 

RAIN TYPES 

Almost all the rainfall may be included under three heads : 
cyclonic, tropical, and monsoon. 

94. Cyclonic Rains. — In the region of the prevailing west- 
erlies, most of the rainfall comes from the cyclonic or low pressure 



74 



ELEMENTS OF PHYSICAL GEOGRAPHY 



areas. As the cyclone moves east across the country, the 
warm, moist winds, moving in from the south and east, ascend 
in the atmospheric whirl and are cooled as they rise ; the 
moisture they carry is condensed and falls as rain or snow. 
The greater part of the rain generally falls to the east or south- 
east of the cyclone center. Verify this by study of the weather 
maps. 

Thunderstorms. — In the summer season the cyclones are 
frequently accompanied by thunderstorms, which are more 




Fig. 39. — Diagram of thunderstorm. (Drawing by W. M. Davis.) 

frequent to the east and south of the cyclone center, but are 
not limited to these parts. They are produced by rapidly 
ascending warm air currents, which produce a heavy cumulus 
cloud, the downward pressure of which causes reversed air 
currents to spread out on the surface in the midst of the as- 
cending warm currents in front of the rapidly moving clouds 
(Fig. 39), The outrushing blast of cool, refreshing air is generally 



THE ATMOSPHERE 75 

followed closely by a downpour of rain which may continue 
for a few minutes or for several hours. Thunderstorms are 
most frequent in the latter part of the afternoon or at night. 

The lightning is caused by the passage of the electric spark from 
cloud to cloud or between the earth and the cloud. Thunder is the 
sound caused by the violent agitation of the air along the flash. Since 
the velocity of light is nearly instantaneous for short distances and 
sound travels about twelve miles per minute or a mile in five seconds, 
the distance of a lightning flash may be roughly estimated in miles by 
dividing by five the number of seconds that elapse between the flash of 
lightning and the sound of the thunder. Much of the rain in the sum- 
mer season in the Mississippi Valley comes from the thunderstorms. 

Cloudbursts, associated with thunderstorms and tornadoes, are 
thought to be caused by ascending air currents so violent that they 
hold up the condensed moisture for some time, until the accumulation 
finally breaks through and the water falls in a mass or sheet, frequently 
causing disaster on the surface where it falls. Cloudbursts are most 
frequent in dry or semi-arid regions, often proving destructive in the 
mountains of Arizona, New Mexico, Colorado, and Southern Cali- 
fornia. Many persons have been drowned from cloudbursts in the 
deserts. 

95. Tropical Rains. — In the doldrum belt tropical rains 
are of almost daily occurrence. The clouds begin to form near 
the middle of the day, and heavy rains, generally accompanied 
by thunderstorms, follow in the early afternoon. The sky clears 
at night and the morning is fair. These rains continue through- 
out the year, shifting north and south with the heat equator. 

96. Monsoon Rains. — These are described in Sec. 82. 

WEATHER 

97. Weather. — Weather refers to all the atmospheric con- 
ditions that can be seen and felt, such as : (1) temperature, 
whether hot or cold, or growing warmer or colder; (2) pre- 
cipitation, whether rain or snow and how much ; (3) cloudi- 
ness and relative humidity ; (4) winds, their direction, velocity, 
and changes. 



76 ELEMENTS OF PHYSICAL GEOGRAPHY 

98. Controlling Factors of the Weather. — In the United 
States and elsewhere in the belt of prevailing westerly winds, 
the daily weather conditions are controlled almost entirely 
by the cyclones and anticyclones. The relative position and 
intensity of these not only determine the weather at the time, 
but enable one, the direction and rate of movement of the 
cyclone being known, to predict the weather conditions for 
some hours or days in advance. 

The following weather conditions may be expected in as- 
sociation with the highs and lows in the United States : " High 
winds with rain or snow usually precede the low. In advance 
of the low the winds are generally southerly and consequently 
bring high temperatures. When the center of a low passes 
to the east of a place, the wind at once shifts to the west or 
northwest, bringing low temperature. The temperature on 
a given parallel west of a low may be reasonably looked for on 
the same parallel to the east when the low has passed. Frost 
will occur along the north of an isotherm of about 40 if the 
night is clear and there is little wind. Following the low 
usually comes an area of high, bringing sunshiny weather, 
which in turn is followed by another low. 

" The cloud and rain area in front of a low is generally about 
the size of the latter and oval, with the west side touching the 
center of the low in advance of which it progresses. 

"When the isotherms run nearly east and west no decided 
changes in temperature will occur. If the isotherms directly 
west of a place incline northwest to southeast it will be warmer ; 
if from northeast to southwest it will be colder. 

' • An absence of decided waves of high or troughs of low 
pressure indicates a continuance of existing weather, which 
will last until later maps show change, usually first appearing 
in the west." 1 

1 Quoted from the chief of the Weather Bureau. 



THE ATMOSPHERE 77 

99. Weather Maps. — At eight 1 o'clock each morning and 
evening, at many places in the United States, Canada, Mexico, 
and the West Indies, observations are made on the weather 
conditions. Reports are also received by wireless telegraphy 
from vessels at sea. A record is made of the barometric pres- 
sure, temperature, velocity and direction of the wind, con- 
dition of the sky, relative humidity, and amount of precipitation, 
and within the hour these data in condensed cipher dispatch 
are sent by telegraph to the Weather Bureau in Washington. 
The data are rapidly tabulated and transferred by appropriate 
symbols to a weather map, this map is in turn engraved, and a 
large edition is printed and delivered to the mails, all within 
a remarkably short period of time. Smaller editions of a less 
elaborate map are prepared at local stations in different cities 
outside of Washington, and printed in one of the local papers. 

The data shown on the weather map consist of (1) isobars, 
represented by solid black lines drawn through points having 
the same atmospheric pressure, a line for each tenth of an inch 
on the barometer ; these lines curve around and inclose the 
lows and the highs ; (2) isotherms, represented by red lines (on the 
local maps, dotted lines), one for each ten degrees difference in 
temperature ; (3) areas, inclosed by heavy, broken red lines, 
where there has been a decided change in temperature equal 
to a rise or fall of twenty degrees or more in twenty-four hours ; 
(4) the condition of the sky, indicated by a small circle, which is 
black for cloudy sky and open for clear sky ; the arrow on the 
circle indicates the direction of the wind ; R signifies rain and S 
snow (Fig. 40) . 

Besides the graphic representation by lines and symbols, all the 
data are printed in tabulated form on the margin of the map. Daily 
weather maps from Washington can generally be secured on applica- 
tion and should be studied along with the text. 

1 Eight o'clock by the 75th meridian time, which means seven o'clock at 
St. Louis, six o'clock at Denver, and five o'clock at San Francisco. 



78 . ELEMENTS OF PHYSICAL GEOGRAPHY 

100. Benefits from Weather Forecasts. — Some of the many 
benefits that may be derived from the widespread distribution 
and heralding of the weather forecasts, are suggested in the 
following. Knowledge of a tropical hurricane in the West 
Indies arrives by cable and wireless and storm signals are placed 
in all the harbors along the Atlantic coast from twenty-four 
to thirty-six hours ahead of the storm, by which information 
many vessels are saved from destruction. Similar forecasts 
of storms save a great many boats on the Great Lakes. Some 
of the insurance companies recognize the value of this branch 
of service by refusing all risks on vessels that go out against 
these warnings. 

The news of a cold wave coming from the northwest causes quite 
a flutter in many lines of business, the ice companies, the coal dealers, 
the railway employees in charge of perishable goods, the fruit com- 
mission merchants, the stock raisers, and many others, who take such 
precautions as they can to prevent loss. It is estimated that $5,000,000 
worth of perishable goods were saved by the warning from the Weather 
Bureau of a single cold wave in January, 1898. An important branch 
of the service consists of the warnings of floods along the larger rivers, 
where the foreknowledge is often the means of saving a great deal of 
property. 

The student may name other ways in which benefit may be derived 
from the foreknowledge of weather changes. 

The weather forecast is given for twenty-four, sometimes 
forty-eight hours ahead. General weather conditions are 
sometimes indicated a week ahead. There has been con- 
siderable study in trying to find some scientific basis of fore- 
telling the weather conditions some weeks or months ahead, 
but without any very satisfactory results. 

CLIMATE 

Climate is the average succession, distribution, and extremes 
of weather conditions for a period of years, in a given region. 
The principal elements of climate are temperature, moisture, 




Fig. 40." — Reduced copy of daily weather map for Feb. 2 and Feb. 4, 1903. 
Note movement of the lows and highs for two days. (U. S. Weather Bureau.) 

79 



80 ELEMENTS OF PHYSICAL GEOGRAPHY 

and winds, and the chief controlling factors are latitude, altitude, 
and relation to oceans and lakes. 

San Francisco and New York have about the same average 
temperature, but the latter has the greater extremes, that is, 
colder winters and hotter summers. Both have about the 
same average rainfall, but in the former it falls in the winter 
months and the summers are rainless, while in New York the 
precipitation is distributed through the year. These two cities 
have quite different climates, despite the fact that both are 
in about the same latitude and altitude, both near the sea, and 
both have about the same annual average temperature and rain- 
fall. 

101. Influence of Forests on Climate. — Forests increase 
evaporation, relative humidity, and cloudiness in the growing 
season. There is some uncertainty as to whether they increase 
the rainfall. They afford protection from winds. 

102. Influence of Mountains. — Mountains, because of in- 
creased altitude, cause lower temperature, greater insolation, 
and radiation, lower absolute humidity, and greater precipita- 
tion up to certain limits. In regions of prevailing winds the 
greater precipitation on the windward slopes is offset by greater 
aridity on the lee slopes. 

103. Influence of Terrestrial Wind Belts. — The belts of 
terrestrial winds are important factors of climatic conditions. 
The doldrum belt has almost daily rains and a uniformly 
warm, moist climate. The trade-wind belt has generally fair 
weather, with continuous, brisk prevailing winds on the seas ; 
while on the land it is characterized by copious rains on the 
windward side of mountains and extreme aridity on the lee 
side. The horse latitude or subtropical belt is characterized 
by fair weather and prevailing calms. The prevailing westerly- 
wind belt, as already described, has a more variable climate 
than any of the others, because of the influence of the cyclones 
and anticyclones. However, the migration of the wind belts 



THE ATMOSPHERE 81 

causes many places to be in one belt part of the year and in 
another belt the rest of the time, thus producing rather marked 
seasonal changes. 

104. Climatic Zones. — The surface of the globe is commonly 
divided into five climatic zones, based on an arbitrary division 
of so many degrees of latitude. Thus the torrid zone includes 
all the area between the tropics, the two temperate zones be- 
tween the tropics and the polar circles, while the remainder is 
in the two frigid zones. It has been shown, however, that the 
unequal distribution of land and water and the mountain ranges 
cause a distribution of winds, rains, and temperature that does 
not follow the parallels. In comparing the isothermal chart 
of the world for the year, and for the winter and summer seasons, 
it will be seen that the temperature inside the tropics in one 
place is quite different from that in the tropics in another place. 
A comparison of the rainfall in different areas shows even more 
marked differences. 

A more practical division of the surface into temperature zones 
would be based on isotherms rather than on the parallels. 
Some of the rather well-defined climatic types that occur in 
different areas are : (1) the doldrums of the tropics, with 
warm, moist climate and persistent rainfall; (2) the trade- 
wind belt, which is warm and wet on the east side of the con- 
tinents and north-south mountain ranges, and generally dry, 
sometimes desert, on the west side of the continent and moun- 
tains; (3) the monsoon belt, with the wet and dry seasons; 
(4) the subtropical belts, over which the dry tropical calms, 
the frequently precipitating trade winds, and the prevailing 
westerlies migrate at different seasons; the temperate zone 
may be divided into two parts: (5) the portions nearer the 
tropics, characterized by warm summers and mild winters, 
and (6) the outer portions, by hot summers and cold winters. 

There" is a marked difference between the climate on the seashore 
and that of the interior, and between the eastern and western shores 



82 ELEMENTS OF PHYSICAL GEOGRAPHY 

of both the continents and the oceans ; likewise between the plain, 
plateau, and mountain climates. Find some examples of each. 

105. Climates and Climatic Regions of the United States. — 
The climate varies greatly in different parts of the United States, 
owing to its great extent, the height and position of the great 
mountain and plateau regions, the relation of different parts 
to the oceans and lakes, and the directions of the winds. The 
whole area of the country might be divided and subdivided 
into climatic regions which would largely correspond to physio- 
graphic regions, since differences in physiography cause dif- 
ference in climate. Some of the more marked variations of 
climatic elements are here enumerated. 

106. Temperature. — The borders of the United States next 
to the sea have in general a more equable temperature than the 
interior portions. The winters are not so cold and the summers 
not so hot, owing to the effect of the water ; such climates are 
called oceanic, in contrast to the continental climate of the in- 
terior. The uniformity is more marked on the western coast 
of the United States than on the eastern, because the prevail- 
ing winds are from the west. It is even more pronounced on 
the oceanic islands, such as Porto Rico, Guam, and the Hawaiian 
Islands. The coast of southern California has the most equable 
temperature conditions of any part of the continental United 
States, rarely rising above 85° in the summer or falling 
below 64° in the winter, a marked contrast with the 
plains of North Dakota, where the yearly temperature range 
is 160 degrees. 

107. Rain. — The coastal regions generally have a heavier 
rainfall than the interior, but it varies widely in different parts 
of the coast. Northwestern Washington has the heaviest 
rainfall, over 150 inches, Florida, the coast of North Carolina, 
and Louisiana have a heavy rainfall, while southwestern Texas 
and southern California coasts have a very light rainfall. 



THE ATMOSPHERE 



83 




84 ELEMENTS OF PHYSICAL GEOGRAPHY 

The rainfall is unequally distributed over the interior country, as 
may be seen by consulting a rainfall map (Fig. 41). There is a 
moderate rainfall, sufficient for the growth of forests and cereals, 
in the middle and eastern portions of the Mississippi basin, but on the 
western part of the basin, over the Great Western Plains between the 
100th meridian and the Rocky Mountains, the climate is semi-arid, 
without enough rain for forests ; farm crops are uncertain unless the 
land is irrigated or dry-farming methods are used. In early days 
this was called the "Great American Desert" and was considered 
worthless, but much of it is now under cultivation, and the remainder 
is used for grazing, as it supports a scanty growth of nutritious grass. 

The Appalachian mountain and plateau area has a humid climate 
and was originally covered with forests. 

The middle slopes of the Rocky Mountains have a moderate rain- 
fall, sufficient to support forest growth. The forests thin out and 
disappear at the base of the mountains, owing to decreased rainfall. 
There are no forests on the high peaks, owing to less rain, more 
snow, and a shorter growing season. 

The plateau areas west of the Rocky Mountains have a scanty 
rainfall, which only on the higher portions is sufficient to support 
forest growth. The basins and lowlands between the Rocky Moun- 
tains and the Pacific mountains have an arid climate, and much of the 
region is desert. The lightest rainfall is in southern Nevada, south- 
eastern California, and western Arizona, portions of which average 
less than five inches per year. The Great Valley of the Pacific, be- 
tween the Cascade-Sierra Nevada Range and the Coast Ranges, 
grades from a humid climate at the north into an arid climate in the 
south. 

108. Seasonal Distribution. — In the California coast and 
valley regions the rain all falls during the winter months, none 
at all in the summer, and the year is divided into the wet season 
and the dry season. On the Great Plains most of the rain falls 
in the summer season. The heaviest rainfall of the southern 
Rocky Mountains and of the western plateaus is in the summer 
season. In most of the agricultural regions outside of the 
irrigated and dry-farming areas, there is some rainfall on about 
one-third of the days of the year. The greatest number of 
rainy days (180) is in northwest Washington. The Great 



THE ATMOSPHERE 85 

Lakes region averages about 170, and the arid districts of the 
southwest about 13. The arid region has a record of 150 
consecutive rainless days, and Washington has a record of 40 
consecutive rainy days. 

109. Snow. — The heaviest snowfall of the United States is 
in the Sierra Nevada-Cascade Mountains. Summit, Cali- 
fornia, has a yearly average of 378 inches. All the railways 
crossing these mountains have a heavy expense for moving 
their trains through the deep snows. The Union Pacific Rail- 
way has built snow sheds over the tracks for 40 miles, and 
during the winter months the trains run under the snow through 
this artificial tunnel. The Great Northern Railway has tun- 
neled through the rocks at the summit of the range and con- 
structed snow sheds for several miles beyond the west end of 
the tunnel. Why the west end and not the east end? On all 
the high peaks of this range snow accumulates from year to 
year, forming permanent snow fields from which flow glaciers 
or streams of ice to lower levels. 

There is a heavy snowfall on the high Rocky Mountains, 
which forms glaciers in Montana, Wyoming, and northern 
Colorado. In the mountain regions of heavy snowfall there 
are numerous snowslides or avalanches, which often prove 
destructive to life and property on the lower slopes. 

The northern peninsula of Michigan has the heaviest snowfall 
(130 inches) of any region of the United States east of the Rocky 
Mountains. Northern New York and New England have heavy 
snows. 

The lowlands of central and southern United States have a light 
snowfall, decreasing towards the south. Southern Florida and southern 
California have no snow. 

110. Winds. — While southwest winds prevail in many 
places, owing to the location in the belt of prevailing westerlies, 
there are many variable winds due to the convectional move- 
ments caused by the cyclones and the anticyclones, land and 



86 ELEMENTS OF PHYSICAL GEOGRAPHY 

sea breezes, and mountain and valley breezes. The tropical 
calm belt extends into the southwestern United States during 
the summer season. In general the high plains and the prairies 
have stronger winds than the forested regions. Coastal regions 
have stronger winds than the interior. The higher mountain 
peaks are also characterized by high winds. 
' Tornadoes of great violence are of frequent occurrence on the 
central plains in the summer season and the gulf plains in the 
spring. Tropical hurricanes are most frequent on the south 
Atlantic coast, but occasionally prove destructive on the Gulf 
coast. The projecting points of land along the Atlantic coast 
at Cape Cod, Cape Henry, and Cape Hatteras are characterized 
by frequent storms and high winds. They are sometimes re- 
ferred to as the " graveyards of the Atlantic," because so many 
vessels are wrecked there by the storms. 

The western plains, valleys, and basins have frequent chinook 
winds from the mountains. These are most frequent on the east 
slopes of the Rocky Mountains and the Cascade Mountains. 

In general the north winds are the cold winds. They are especially 
prominent in Texas, where they are called northers. South winds are 
generally warm ; east winds in the eastern United States are generally 
raw, penetrating winds in the spring and winter season, and sultry, 
oppressive winds in the summer season, because the relative humidity 
is high. They are commonly accompanied by cloudy skies and rain. 

111. Changes in Climate. — One frequently hears the state- 
ment that the climate is changing — that the winters are not 
so cold and there is not so much snow as there was years ago. 
It. is not the climate but the weather which varies from year to 
year. Some winters are colder than others, some summers 
are drier than others, a difference frequently quite marked 
between successive seasons ; but the average for a number of 
years does not change perceptibly. The official weather 
records extending back more than fifty years do not indicate 
any noticeable change in climate. 



THE ATMOSPHERE 87 

112. Geological Climates. — The geological record, which, ex- 
tends over millions instead of a few tens of years, shows many pro- 
nounced climatic changes. For instance, some few tens of thousands 
of years ago the climate was enough colder than at present in the 
northern hemisphere, to cause an accumulation of snow and ice in 
the form of great glaciers over all the north central parts of North 
America and Europe. This condition continued apparently for many 
thousands of years. In a preceding geological period it was warm 
enough for the growth of tropical plants as far north as the Arctic 
Circle. 

In still earlier geological times, millions of years ago, the climate of 
central New York and southern Michigan was exceedingly dry, pos- 
sibly as dry as that of Utah today. This is shown in the record by 
the great beds of rock salt in this region. 

Changes in climate are caused by changes in physical geography. 
Thus the elevation of mountain ranges or plateaus, or the lowering 
of such areas by erosion, produce changes in temperature, rainfall, 
and the movements of the winds, but such changes are slow, involving 
periods of hundreds of thousands of years, as interpreted from the 
geological record. 

Changes in climate may also be caused by a change in the com- 
position of the atmosphere. For instance, an increase in the amount 
of carbonic acid gas in the atmosphere would make it warmer and a 
decrease would make it colder, but such a change would result from a 
geographic change and would involve a long period of time. 

It is thought by some that astronomic changes, such as a change 
in the earth's orbit accompanied by a shifting of the seasons, produce 
climatic changes. 

The geological record seems to show conclusively that great cli- 
matic changes have taken place in the remote past, but there is still 
some uncertainty as to the causes of such changes. 

QUESTIONS 

1. Name all the Junctions of the atmosphere. 

2. Name all the constituents of the atmosphere and the relative 
amount of each. 

3. What would be some of the effects of doubling the percentage 
of oxygen in the air ? 

4. What would be the effect if there were twice as much carbonic 
acid gas in the air ? If there were half as much ? 



88 ELEMENTS OF PHYSICAL GEOGRAPHY 

5. Why is the air on the mountains much clearer than on the 
plains ? 

6. Why can one exercise more vigorously at the base of a high 
mountain than at the top ? 

7. Explain how a barometer is used in measuring the height of 
mountains. 

8. Why is a mercury barometer more reliable than an aneroid ? 

9. Explain the relation of a common pump to a barometer. From 
what depth can water be raised by a common pump ? 

10. How high is the atmosphere ? 

11. Explain how you could make a pressure curve. If j r ou have 
access to a barometer, make a pressure curve. 

12. Why are there more isobars on some weather maps than on 
others ? 

13. If you put a block of ice in a vessel over the fire, how warm 
can you make it ? What becomes of the heat ? 

14. Why does sprinkling the pavement on a summer day cool the air ? 

15. Why is it generally cooler after a rain in the summer ? 

16. Sometimes it is warmer after a shower. Why? 

17. What is the reason for the statement sometimes made in the 
winter, "It is too cold to snow"? 

18. Generally it is warmer in the afternoon than at noon. Why? 

19. Sometimes it is colder at noon than in the morning. Why ? 

20. Why is black soil warmer than light-colored soil ? 

21. If you should take a stick of green wood and an iron poker, 
and thrust one end of each into the fire, which one would become 
hottest a foot away from the fire ? Why ? 

22. When ice freezes on a lake, is the air over the newly formed 
ice made colder or warmer? Why? 

23. There is as much sunshine in a year at the north pole as at the 
equator. Why is the air not as warm ? 

24. Why is it colder on a mountain than on the bordering plains ? 

25. Why is Minneapolis sometimes warmer in the summer than 
Key West ? Why is it colder in the winter ? 

26. Why do spring flowers bloom earlier on the north side of an 
east-west valley than on the south side ? 

27. Why are summer isotherms farther from the equator on the 
continents than on the oceans? 

28. Why is the air in a heated room always warmer at the ceiling 
than at the floor? Why is the air generally warmer near the surface 
of the earth than it is a few miles above the surface? 



THE ATMOSPHERE 89 

29. Why are trade winds more constant in direction than the pre- 
vailing westerly winds? 

30. Why do cyclones cause more rain than anticyclones ? 

31. Why does a falling barometer indicate an approaching storm? 

32. Why do the West Indian hurricanes first move northwest and 
then northeast ? 

33. Explain how a tornado differs from a cyclone. How does 
each differ from a hurricane? 

34.- Why are windows generally blown out rather than in during a 
tornado ? 

35. Since corn requires warmth, why do the hot waves frequently 
destroy much corn in the corn belt ? 

36. Boulder, Colorado, is at the eastern base of the Rocky Moun- 
tains ; which direction should you expect the winds to blow in the fore- 
noon ? 

37. Why are there more windmills on the plains and prairies than 
in the hill and mountain areas ? State two good reasons. 

38. With a cyclone center near St. Louis on July 3, forecast the 
probable weather conditions for July 4 at Pittsburg, and at Kansas 
City. 

39. Why are there more cloudbursts in Arizona and southern 
Colorado than in New York or Virginia ? 

40. Why is there a greater rainfall at Asheville, North Carolina, 
than at Pittsburg, Pennsylvania? Why more rain at Seattle than 
at San Diego ? Why more rain at St. Louis than at Santa Fe ? 

41. Why is it colder in the winter at St. Louis than at Norfolk, 
Virginia? Why colder at St. Paul than at Portland, Oregon? 

42. Why are the chinook winds dry ? Why warm ? 

43. Why are storms from the southwest called "northeasters"? 

44. Why do stoves and fireplaces sometimes smoke when the fire 
is first started ? 

45. Why does wet cloth feel colder than dry cloth ? 

46. Why do tornadoes occur most frequently in the afternoon ? 

47. Why are thunderstorms, so common in the east, almost un- 
known in California ? 



CHAPTER III 
THE OCEAN 

A pew centuries ago the ocean was an impassable barrier to 
man ; now it is a great international highway, the greatest and 
best in the world. The first great factor in changing this barrier 
to a highway was the mariner's compass, the second was the 
steamboat (although the barrier was crossed before the days of 
steam) . 

Man now crosses the ocean in a floating palace, yes, even in 
a floating city. One can now enter one of the ocean liners at 
the Atlantic seaboard, with nearly as many people as inhabit 
the capital city of some of our western states, and after a few 
days of life of comfort and luxury find himself on the other 
side of the ocean. These floating cities carry their own 
electric-light plants, water works, swimming pools, theaters, 
bowling alleys, dining rooms, sleeping rooms, parlors, stores, 
and daily newspaper. They have almost constant communica- 
tion with the rest of the world, by means of wireless telegraphy. 
In fact one can have almost every comfort and luxury obtain- 
able in a city of 8000 people on the land. One can now travel 
on regular lines of steamers between all the important seaports 
of the world and go to a point across the ocean more quickly 
and comfortably than he could have crossed the United States 
a few years ago. 

The ocean highway differs from all land highways in that it is open 
to all nations, and in that it is free from all grades, not a hill nor a 
mountain to cross anywhere. 

90 



THE OCEAN 91 

During the World War this great ocean highway was menaced in 
many places by the German submarine boats, which, contrary to in- 
ternational law and the law of humanity, sank ocean steamers wherever 
they could. This danger ceased with the end of the war. 

Other features of the ocean that make it valuable to man are : 
(1) it is the source — by evaporation and through distribution 
by the winds — of all the water that waters the land ; (2) by 
movements of large volumes of its water it tempers the climates 
of the land by carrying warm waters into cold regions and cool 
waters into warm regions ; (3) the fish and other forms of life 
in its waters supply mankind with vast quantities of food and 
other necessities. 

The surface of the ocean is more nearly level than any other 
large part of the earth's surface, and hence it is taken as the 
base from which elevations on the land are reckoned. While 
the surface of the ocean is assumed to be level in determining 
elevations, it is now known that it is not level. It is higher 
along the shore, especially along shores bordered by high moun- 
tains and plateaus, owing to the gravitative attraction of the 
land masses. It is also higher at the equator than at the poles, 
owing to rotation. There are also many inequalities due to 
tidal waves and strong winds. 

Scientific exploration in recent years has given to the world much 
definite knowledge concerning the depth, temperature, deposits, and 
life of the deeper parts of the ocean bottom. The Challenger expedition 
sent out by the British government, the voyages of the Blake, the 
Albatross, and other vessels, by the American government, the ex- 
plorations of the Duke degli Abruzzi, of Alexander Agassiz, and others, 
have all done much valuable work in oceanography. 

113. Divisions of the Ocean. — The ocean is a continuous 
body of salt water surrounding the continents and islands. 
The parts between the continents are partly surrounded by 
land areas and are distinguished on the globe and maps of the 
world by separate names. The part of the ocean east of the 



92 



ELEMENTS OF PHYSICAL GEOGRAPHY 



western hemisphere is named the Atlantic, and that on the 
west, the Pacific ; these are sometimes further divided into 
North Atlantic, South Atlantic, North Pacific, and South 
Pacific, with the equator as the dividing line. An arm of the 
Pacific Ocean partly surrounded by Africa, Asia, Australia, 
and some of the East India Islands is called the Indian Ocean. 
The part of the ocean around the North Pole is called the Arctic 




Water Hemisphere. 



Land Hemisphere. 



Fig. 42. — Division of the earth into two hemispheres, one of which contains 
nearly all the land. London is near the center of the land hemisphere. 



Ocean or the North Polar Sea. It is the most isolated portion 
of the ocean, owing to the near approach of the continents to 
each other in the northern hemisphere. 

The South Atlantic and South Pacific open southward, com- 
pletely encircling the earth about latitude 60° S. The southern 
part of this encircling sea, inside the Antarctic Circle, is called 
the Antarctic Ocean or the South Polar Sea ; there is no land 
barrier bordering this division of the ocean, but it entirely sur- 
rounds the Antarctic continent, the land mass at the South Pole. 

The equator does not equally divide either the land or the ocean 
areas. More than half the land lies north of the equator, more than 



THE OCEAN 93 

half the ocean lies south. The unequal division of land and water is 
more strongly marked when the earth is divided into two hemispheres 
by taking London as the center of one hemisphere and a point in the 
South Pacific Ocean as the other. The London hemisphere would 
include about nine-tenths of all the land areas and might be called 
the land hemisphere, and the other might be called the water hemi- 
sphere ; even then the land hemisphere would be more than half water 
surface, but the water hemisphere would be about fourteen-fifteenths 
water (Fig. 42). 

114. Size of the Ocean. — The ocean covers nearly three 
times (72 per cent) as much of the earth's surface as does the 
land. It has an area of 143,259,000 square miles, about one- 
fourteenth of which is continental shelf (See Sec. 118) and the 
remainder ocean basin. The volume of the ocean is approxi- 
mately fifteen times as large as the volume of land above sea 
level. It is estimated that there are 1300 million million gallons 
of water in the entire ocean. 

115. Composition of Sea Water. — Sea water contains much 
mineral matter in solution, the average being about 3.5 per 
cent, but it varies considerably in different parts of the ocean. 
The inflow of a great river like the Amazon or the Mississippi, 
or excessive evaporation in certair localities, produces local 
variations in the percentage of salt. About three-fourths of 
the mineral matter held in solution is sodium chloride or common 
salt. The remainder consists largely of magnesium, calcium, 
and potassium salts. There are minute quantities of other 
elements. 

Chemical composition of the salts of average sea water : 

Sodium chloride (NaCl) 77.758% 

Magnesium chloride (MgCl 2 ) 10.878% 

Magnesium sulfate (MgS0 4 ) 4.737% 

Calcium sulfate (CaS0 4 ) 3.600% 

Potassium sulfate (K 2 S0 4 ) 2.465% 

Calcium carbonate (CaC0 3 ) 0.345% 

Magnesium bromide (MgBr 2 ) 0.217% 



94 ELEMENTS OF PHYSICAL GEOGRAPHY 

Besides the solid salts dissolved in the sea water there is a large 
quantity of the gases of the atmosphere, which, like the salts, vary- 
greatly in quantity in different parts of the ocean and in the same part 
at different times. Fish and other animals of the sea obtain the 
oxygen necessary for life from the sea water. 

The carbonate of lime in limestone beds on the land is dissolved 
by carbonic acid in the ground water and carried into the sea in solu- 
tion. When corals and other animals and plants secrete the lime 
carbonate in their skeletons or shells, the carbonic acid that was hold- 
ing it in solution is set free and part of it goes back into the atmosphere. 

116. Circulation of the Salts of the Ocean. — The water 
flowing into the sea carries salts in solution, while that which 
is evaporated is nearly pure water. Apparently this would 
cause an accumulation of salts in the ocean. On the other 
hand, it is probable that many of the salts carried to the ocean 
are those that were formerly taken from the ocean. The salt 
in the great beds in central New York and elsewhere was 
formerly in solution in the ocean. Nearly all the great beds 
of limestone over all the continents were deposited in the sea . 
from materials taken from solution, and they are now being 
returned to the sea, to be again extracted from the solution 
by animals and plants to form new beds of limestone over the 
sea bottom. Therefore the salts, like the water, circulate 
from the ocean to the continents and back, and it is not possible 
from our present knowledge to say whether the sea water is 
becoming denser or not. 

117. Topography of the Ocean Bottom. — The broader 
general features of the ocean bottom are not greatly different 
from those of the land areas, but the details are decidedly 
different. There are plains, plateaus, and mountains, but there 
is an almost total lack of valleys and hills that mark the con- 
tinental land areas. Hence, if the sea bottom were exposed 
to view, one would be impressed by the striking monotony 
of the scenery, and the absence of many varied forms sculptured 
on the land by rainfall, winds, and streams. 



THE OCEAN 



95 



In places on the continental shelf where portions of the land area 
have been recently submerged, the buried hills and valleys are not en- 
tirely obliterated. 

Depressions on the continental shelf extending out from the Hudson, 
Delaware, and Susquehanna Rivers indicate the former extension of the 
valleys of these rivers over what is now the continental shelf, when 
it was land area and the shore was farther east than at present. 

118. The Continental Shelf. — The part of a continental 
border covered by the ocean is called the continental shelf. 
It ranges in width from a fraction of a mile to more than a 



-r-^-rT^XONTINENT 


7^ K CONTINENTAL SHELF 




§§§§§§ 


'MM^^^^ 


w OCEAN BASIN 


^^m^mw 


y///////9^^/^ 



Fig. 43. 



Vertical section across a continental shelf showing its relation to 
the continent and ocean basin. 



hundred miles. From the outer or ocean margin of the shelf 
there is a slope or descent down to the ocean depths, forming 
the sides of the basin. In other words, the ocean basins are 
full to overflowing and the overflow extends out over the border 
of the land areas, forming an irregular belt of shallow water, 
the continental shelf, which corresponds in a way to an irregular 
rim of the submerged basin. The water area of the continental 
shelf varies from time to time, owing to warping movements 
of the earth's crust which cause elevations in some places and 
depressions in others. (See Chapter XL) A depression of 
the continents or a rising of the ocean bottom causes a further 
advance of the water on the land, and the continental shelf is 
wider. An elevation of the land area or a sinking of the sea 
bottom causes the recession of the shore line and the emergence 
of the shallow sea bottom ; the -continental shelf is narrower 
and the continent larger. Considerable portions of all the 



96 ELEMENTS OF PHYSICAL GEOGRAPHY 

continents have in ages past been covered by the sea and formed 
part of the continental shelf during the submergence. (See 
Fig. 43.) 

119. The Deeps. — Inside the bordering continental shelf 
lie the great ocean basins, on the bottom of which in many- 
places are deep depressions known as deeps, extending in some 
cases many thousands of feet below the general level of the 
ocean basin. 

Some of the ocean deeps extend farther below the level of 
the sea than the highest mountains and plateaus extend above 
it. The Challenger deep, near the Island of Guam, is 31,600 
feet below the sea level ; another, near the Ladrone Islands 
in the North Pacific, is 31,614 feet deep. The Aldrich deep, 
northeast of New Zealand, is 30,830 feet deep. The Tuscarora 
deep, east of Japan, is nearly 28,000 feet deep. The Planet deep, 
about 40 miles north of Mindanao, P. I., is 32,078 feet deep. 

The deepest sounding in the Atlantic Ocean is the Blake 
deep, 27,366 feet. There are few other places in the Atlantic 
Ocean known to be more than 20,000 feet deep, nor are any 
known in the Indian or southern oceans more than 20,000 feet. 
Hence, so far as known, the deepest deeps are in the largest 
oceans. 

120. Mediterraneans. — Besides the open ocean there are 
several smaller divisions partially separated from it, the largest 
of which is the Mediterranean Sea, whose depth is nearly as 
great as that of the great oceans. It is almost entirely separated 
from the open sea, being connected with the Atlantic Ocean 
by the narrow strait of Gibraltar and with the Indian Ocean 
by the Suez Canal, and the Red Sea. 

Other mediterranean seas are the Gulf of Mexico and the 
Caribbean, China, and Japan Seas. Although the surface por- 
tions of these are not as nearly surrounded by land as the 
Mediterranean Sea, yet their .deep basins are surrounded by 
land. 



THE OCEAN 97 

The extension of shallow sea areas over the interior portions 
of the continents, such as formerly covered the area of the 
central Mississippi basin and later the area of the Great Western 
Plains, are called epicontinental seas. Hudson Bay is now an 
epicontinental sea. 

121. Stability of Sea Basins and Continents. — Despite the 
fact that the continents are for the most part covered with sea-bottom 
deposits, there is good reason for thinking that there is little or no 
change from sea basin to land area and vice versa. The interchange 
has been between the continents and the continental shelf. At the 
present time the area of the continental shelf is about 10,000,000 
square miles. From time to time portions of it are elevated above 
the sea level and added to the continents, and portions of the continents 
are depressed and added to the sea area. Warping movements (Com- 
pare first part of Chapter XI) of this kind have produced many changes 
in the land and sea areas during the past geological ages. Through 
them all, the continents have probably been growing larger and the 
continental shelf smaller. The ocean basins have probably grown 
deeper, but, so far as known, not much larger or smaller in area. 

122. Sounding and Dredging. — Much definite knowledge 
concerning the ocean, especially the deeper portions, has been 
gained in the last half century by improved methods of sound- 
ing and dredging. Previous explorations of the sea had been 
largely devoted to delineating the shore lines of the continents 
and islands. With the adoption and improvements of modern 
sounding and dredging methods a new field of investigation 
was opened, namely, the bottom and the deep waters of the 
ocean basirjs. 

Soundings are made with fine steel wire (why not rope?) 
to which a sinker in the form of a heavy iron ball like a cannon 
ball is attached in such a way that it is released when it strikes 
the bottom. Why are the sinkers left on the bottom of the 
ocean?- Samples of water are obtained from different depths 
by attaching to the wire at definite intervals brass tubes, 



98 



ELEMENTS OF PHYSICAL GEOGRAPHY 



called water bottles, so constructed that they remain open in 
descent but are automatically closed as soon as lifting begins 

(Fig. 44). 

The temperature of the 
ocean deeps is obtained by 
self-recording thermometers. 
These, like the water bottles, 
are attached to the line at 
different places, so that a 
single sounding gives not only 
the depth, but also samples 
of the water and the tem- 
perature at several different 
depths below the surface. 
Moreover, a sample of the 
bottom mud may be obtained 
at the same time by collect- 
ing that which sticks to the 
water bottle at the bottom 
end of the wire. Another 
form of sounding apparatus 
has a small cup at the bottom 
which closes automatically 
when lifted from the bottom 
ooze and brings up a sample 
of the bottom mud. 
Specimens of the bottom sediment are generally obtained, 
along with specimens of the life, in trawls or dredges, consisting 
of strong nets having an iron rim and laden with weights. 
These nets when dragged along the sea bottom scoop up masses 
of soft mud, ooze, and specimens of such forms of life as there 
exist (Fig. 45). 

There is another method of sounding, by meaDS of an instru- 
ment which records the pressure. One advantage of this 



W 



"ZT 



Fig. 44. 




- Diagram of sounding 
apparatus. 



THE OCEAN 



99 



method lies in the fact that it can be used without stopping 
the vessel, as it is independent of the length of line. 

123. Deposits on the 
Continental Shelf. — 
The materials on the sea 
bottom are quite varied 
in different places, but 
may be divided into 
(a) those on the conti- 
nental shelf and (b) 
those over the deep-sea 
basins. The first in- 
clude those deposited in 
water less than 600 feet 
deep, and consist of 
gravel, sand, mud, and 
coral and other lime- 
stones, the materials of 
which are derived 
mainly from the land 
areas. 

The materials eroded 
from the land by the 
rivers and from the 
beach by the ocean 
waves, are carried out 
and spread over the sea 
bottom by the river and 
shore currents, by the 
undertow, and by winds 
which carry them as dust through the atmosphere. The sand 
and mud are carried in suspension and dragged along the 
bottom, while the lime carbonate for the limestones is carried 
out in solution. 




Fig. 45. — Two types of dredges used in 
collecting specimens of mud and life forms 
from the bottom of the ocean. 1, Chester 
rake dredge. 2, Blake dredge. (U. S. Fish 
Commission.) 



100 ELEMENTS OF PHYSICAL GEOGRAPHY 

The mechanical sediments are generally coarser and thicker within 
a few miles of the shore, thinning out in the deeper waters, although 
fine muds form in places in shallow water where there are no strong 
currents to distribute them. The calcareous or limestone deposits are 
formed in the clearer waters, which are comparatively free from 
sediments. 

The greater part of the continental areas is covered with rocks 
that were formed in the sea. Even great mountain ranges and ex- 
tensive plateau areas are largely composed of materials deposited on 
a former continental shelf, for they contain fossil remains of animals 
that live only in the ocean. It is quite probable that the portions 
of the present sea over the continental shelf may in the future become 
land areas not greatly different from the present lands. 

Most of the rocks over the continents consist of sandstones, 
shales, and limestones, the off-shore shallow water deposits ; 
yet there are representatives of the oozes in the chalk beds of 
England, France, and portions of the United States. There 
are diatomaceous deposits of great extent in California, Nevada, 
and elsewhere, and of greensand maris in New Jersey and 
Maryland. 

124. Deposits in the Sea Basins. — The deeper portions of 
the sea — the deep basins outside the continental shelf — are 




Fig. 46. — Microscopic view of deep-sea ooze. A. Foraminifera (calcareous! 
ooze magnified 50 diameters, from depth of 11,000 feet. B. Radiolarian 
(siliceous) ooze magnified 100 diameters, from depth of 26,580 feet. 



THE OCEAN 



101 



covered with organic oozes and fine muds. Some of the oozes 
are calcareous or limy, and some siliceous, that is, composed 
of silica. The most common of the calcareous oozes, named 
from the prevailing forms of organic remains, are the globigerina 
ooze and the pteropod ooze ; the siliceous ones are the radiolarian 
ooze and the diatom ooze. The first three organisms are minute 
animal forms (Fig. 46) ; diatoms are microscopic plants of 
varied and beautiful forms which live in both salt and fresh 
water. (See Figs. 47 and 248.) 




Fig. 47. — Mountains formed of diatom ooze at Lompoc, Calif. 
(Photo by the author.) 



The microscopic plants and animals which form the different oozes 
live abundantly on or near the surface of the sea; as they die, their 
remains sink to the bottom and accumulate as the soft ooze. They 
live at the surface in shallow water as well as in mid-ocean, but there 
is so much other material on the bottom of the shallow seas that the 
remains of the microscopic organisms are generally obscured, while 
in the deep sea they form the bulk of the material on the bottom. 



102 ELEMENTS OF PHYSICAL GEOGRAPHY 

In many places around the border of the oceanic basins there 
are extensive areas of fine muds, named from their color, blue, 
red, and green. In the deepest portions of the sea basins, 
known as the deeps, the bottom is covered with red clay, the 
origin of which is uncertain, but it is probably formed, in part 
at least, of volcanic and meteoric dust. Glauconite or green- 
sand covers the sea bottom in some places. 

It is estimated that the red-clay areas of the sea bottom cover 51 
million square miles ; foraminif eral ooze 50 million ; diatom ooze 
11 million; radiolarian over 2 million; and glauconite or greensand 
1 million square miles. 

MOVEMENTS OF SEA WATER 

125. Waves. — Waves are formed on the surface of the sea 
or -any other body of water by the friction of the wind blowing 



Fig. 48. — Diagram illustrating movement of water particles in waves. 
The water rises in front of the advancing wave and sinks after the passing of 
the crest of the wave, each particle traversing a circular or elliptical path. 

across it, causing the surface water to oscillate up and down, 
and back and forth, each particle of water following a somewhat 
elliptical path (Fig. 48). Generally the backward movement 
equals the forward movement and the water comes to rest 
where it started, without any forward motion, except where 
the wave curls and breaks, when the top of the wave is driven 
forward and a surface current is started. If the wind continues 
for some time with sufficient force to form breakers or white- 
caps, considerable quantities of water may be driven forward 
and heaped up on the windward shores or form currents in the 
open sea. 



THE OCEAN 103 

Size of Waves. — The stronger the wind the larger the waves 
that are formed. The height of waves, measured from the 
bottom of the trough to the top of the crest, is sometimes thirty 
feet or more, rarely reaching a height of fifty feet in the open 
sea. The length of waves varies from a few feet to 1500 feet or 
more, much more in the earthquake waves, and the velocity 
varies from twenty to sixty miles an hour. The visible side of 
an advancing wave is the front, the opposite side the back of 
the wave. 

The size of a wave increases with the density, area, and depth 
of water ; hence the ocean waves are larger than those on lakes 
or rivers. 

Waves formed in a storm often extend far beyond the storm area 
into regions of light winds and calms. Such waves are known as the 
ground swell and, probably because of their greater regularity and 
monotony of motion, are more productive of seasickness than the 
storm that produces them. 

126. Breakers. — As the waves of the open sea approach 
the shore, where there is not sufficient depth of water to form 
the front of the advancing wave, the top moves forward, breaks 
off, and falls as foam to be caught by the advancing wave and 
carried forward until the wave breaks again, in this way form- 
ing the so-called breakers along the shore. It is these breakers 
that are so destructive to boats and other property. Hence, 
when vessels cruising along the shore find a storm coming, if 
there is no good harbor near at hand, they sail for the open sea, 
to avoid the destructive breakers of the shallow water. The 
white foaming water produced by the breakers is called surf, 
which, when not too violent, is attractive to surf bathers 
(Fig. 49). 

127. Undertow. — The undertow is a backward movement 
along the bottom from the shore towards the open sea. The 
water that is carried forward and heaped up on the shore by the 
breakers cannot return seaward on the surface because of the 



104 



ELEMENTS OF PHYSICAL GEOGRAPHY 



incoming waves, so it flows along the bottom, forming the 
undertow which so often proves dangerous to surf bathers, 
who are caught by it and carried out into deep water and 
drowned. Fine material that is ground up by waves on the 
beach is carried back into deeper water by the undertow and 




— l lHHMB»iif N 









Fig. 49. — Breakers and surf on a boulder beach. (Photo by M. S. Lovell.) 

spread out in beds of gravel, sand, and clay which may later be 
elevated and form part of the stratified rocks of the continent. 

128. Effects of the Waves. ■ — (1) One of the most con- 
spicuous effects of the waves is the modification of the shore 
line produced by the erosive action. In this work the common 
wind and storm waves are assisted by the tidal and the earth- 
quake waves. They wear away rocks in some places and build 
up bars and reefs in others. The softer rocks are worn away 
first, forming bays and inlets between the harder rocks, which 
form the headlands, or in some cases islands (Fig. 50). 

(2) The waves aerate the waters of the ocean by stirring 
them up and thus exposing larger surfaces to the action of the 



THE OCEAN 105 

atmosphere ; also by blowing over the crests of the waves, thus 
inclosing the air in the waters. This action serves to oxidize 
the decaying organic matter and thus purify the waters ; it 
also furnishes oxygen for the animals living in the sea. 




Fig. 50. — Wave-eroded rocky shore, Pacific Coast. (Photo by Detroit 
Publishing Co.) 

(3) The waves exercise enormous mechanical power, part 
of which is utilized by man to ring the bell and blow the whistle 
on the harbor buoys. This power is sometimes also used to 
pump water, or open floodgates. 

' (4) The waves are frequently destructive to life and property. 
During violent storms they destroy sea walls, docks, lighthouses, 
and other property on shore, and frequently overwhelm and 
destroy boats. The destructive effect of the waves on boats 



106 ELEMENTS OF PHYSICAL GEOGRAPHY 

in the open sea is materially lessened, the vessel often is saved, 
by spreading a little oil on the water. The disastrous effects 
of the waves are produced by the breaking of the wave, when 
the top curls over and falls upon the boat. A little oil on the 
water spreads rapidly even in the face of the wind, and de- 




Fig. 51. — Low tide, Bay of Fundy. See Fig. 52. (Photo by Roland 
Hayward, 1903.) 

creases the friction enough to permit the crest of the wave to 
settle back quietly without breaking. Small boats can safely 
ride the largest waves as long as the waves do not break and 
fall into the boat. 

129. Tides and Tidal Waves. — At all points on the shore 
of the ocean the water rises and falls twice each day. It rises 
steadily for about six hours until it reaches its highest level, 
high tide, and then subsides for about six hours, until it reaches 



THE OCEAN 107 

its lowest level, low tide, when it again rises. The period of 
rising is not always uniform with the period of falling, but the 
average of the sum of the two is equal to 12 hours and 26 minutes 
(Figs. 51 and 52). 
Twice each month the tides reach a maximum height, the 



Fig. 52. — High tide, Bay of Fundy. See Fig. 51. (Photo by Roland 
Hayward, 1903.) 

spring tide, and twice each month they reach the minimum 
height, the neap tide. The incoming tide is called the flood 
tide, the outgoing the ebb tide. Slack water is the interval be- 
tween the two. 

In shallow harbors the hour of the ' departure of ocean steamers 
is usually determined by the time of high tide, as they can then float 
with safety over the bars and shallow places which they could not 
pass at low tide. Finding the time when high tide will occur at any 



108 ELEMENTS OF PHYSICAL GEOGRAPHY 

place is called "establishing the port." It is the interval between 
the passage of the moon across the meridian and the next high tide. 
At New York it is 8 hours and 13 minutes. The time interval and the 
height of tides vary greatly at different ports. 

On the open sea the rise and fall of the tide is not perceptible, so 
low and broad is the wave. In bays and estuaries having a wide 
opening to the sea, where the advancing tidal wave is gradually con- 



I^Mwiwfcfawm^-..- „. - 






..... --'nirifi ilnii' 




jjfifcv ■ (fL •■. 


:«.; „■: "i- 


^^wW5^^"C^jS'***^^ r! »' • "~~?t**— « 








•■-">:■ '-« 


-■ •*■*■ ■ --' ' '.' 


\"i~'~ ' ■','•' ■■'-'•.*" ' .' ^ -■■-■■ '"" 






sSr- .. - --v-".''V- . 







Fig. 53. — Tidal flats. Low tide in Basin of Minas, N. S. The area is 
covered with water at time of high tide. (Photo by S. R. Stoddard.) 

fined and restricted, it frequently rises to great heights. In the Bay 
of Fundy, on the coast of Nova Scotia, the tide rises to a height of 
50 feet or more. Similar high tides occur in the Bristol Channel. 
In both places the tide is not conspicuously high at the comparatively 
wide mouth of the bay, but as the low, long wave advances up the 
ever-narrowing channel the waters continue to pile up until they 
reach a maximum at or near the head of the bay (Figs. 51 and 52). 
Where the coast is low there is a broad area exposed between high and 
low tides, called tidal flats (Fig. 53). 

Broad gulfs and bays connected with the sea by a narrow opening 
have comparatively low tides. There is considerable variation in 
the height of tides in different places along the coast. 

130. Tidal Wave in Rivers. — In certain places the tidal 
wave meets opposition in the current of the river and at times 



THE OCEAN 109 

the waters rise in a high wave commonly known as a bore or 
eagre, which rushes up the river, often with high velocity, 
causing great destruction along the banks and at times to 
shipping in the river. On the Amazon River this tidal wave, 
known as the pororoca, extends up the river for several hundred 
miles, with great destruction to the bordering forests. Similar 
waves often prove very destructive to shipping on the Hoang 
Ho (River) in China. On the Seine River, in France, the wave 
is called the mascaret. 

131. Cause of the Tides. — The interval of time between suc- 
cessive high tides is 12 hours and 26 minutes, just half the interval 
of one lunar day, 24 hours and 52 minutes. This led to the conclusion 
that in some way the moon was the cause. A complete explanation 

C 





D 

Fig. 54. — Diagram illustrating the origin of tides. 

of the tides is involved in higher mathematics, but a fair idea of the 
movement may be gained if one comprehends the combined results 
of three forces or conditions acting simultaneously : 

(1) The universal law of gravitation — that every particle of 
matter in the universe is attracted by every other particle directly 
in proportion to its mass and inversely as the square of the distance. 

(2) The law of inertia — that a body once set in motion will con- 
tinue in motion unless changed by some other force. 

(3) The fact that the particles of water move much more freely 
among themselves than the particles of the more rigid rock. 

Each particle of matter on the surface of the earth, as at A, B, C, 
and D in the diagram (Fig. 54), by the law of gravity is pulled towards 



110 ELEMENTS OF PHYSICAL GEOGRAPHY 

the center of the earth and also towards the center of the moon ; by 
the law of inertia it tends to move in a straight line tangent to the 
earth. 

The gravitative pull of the moon is stronger at A than at any other 
point on the surface of the earth because it is nearer, hence the move- 
ment of the water particles toward M forms a tidal wave at A. The 
pull of the moon at B is less than at any other point, hence the inertia 
of the water at B is greater than at any other point, causing it to rise 
in a tidal wave. 

The rising of the water to form the high tides at A and B causes 
corresponding low tides at C and D. 

The sun also causes tides on the earth, but they are so much smaller 
than those caused by the moon that they are rarely noticed except 
when they coincide with those of the moon or are directly opposed to 
them, when they cause the spring or neap tides. 

132. Spring and Neap Tides. — The sun tide coincides with 
the moon tide when the sun and moon are in line with the earth, 
either on the same side, as at new moon, or on opposite sides, 
as at full moon. The tides are then equal to the sum of the 
two, the greatest for the month, and are called spring tides. 

During the first and third quarters of the moon the sun and 
moon are at right angles to each other from any point on the 
earth, at which time the tide equals the difference between the 
two and hence is the lowest for the month, the neap tides 
(Fig. 55). 

Owing to the inertia of the water, it takes some time for the full 
effect of the moon's attraction to manifest itself, so that high tide is 
not directly underneath the moon, but some distance, at times some 
hours behind it. The regularity of the movement of the wave is dis- 
turbed very much by the continental and insular land masses, and in 
straits, so that in many places the tidal movements become quite 
complex. 

133. Effects of Tides on the Shores. — The tides usually 
advance on the shore in a series of waves that affect the shore 
like other waves. In addition the change of level of the ocean 



THE OCEAN 



111 



waters during high tide and low tide causes the waves, both 
tidal waves and storm waves, to strike the shore at different 
elevations, thus widening the zone of erosion. Among islands 
and in the straits the tide produces currents (called tidal races) 
which are sometimes effective agents of erosion and a menace 
to navigation. In Long Island Sound a low tide from the east 



Q© 

o. 








Fig. 55. — Diagram showing relative position of the sun, moon, and earth 
during spring tide (A) and neap tide (B). 

meets a high tide from the west at Hell Gate and six hours 
later the conditions are reversed. At both times the tidal 
current, or race, rushing through the narrow rocky channel 
with great velocity, proved destructive to shipping until the 
channel was widened by blasting away the rocks. A some- 
what similar but more complex meeting of the tides in the North 
Sea, between Great Britain and the continent, forms the 
dreaded Maelstrom. 

The sloughs or boat channels across the tidal marshes border- 
ing the Bay of San Francisco (See Fig. 56) and the thorofares 



112 ELEMENTS OF PHYSICAL GEOGRAPHY 




Fig. 56. — Tidal channel near mouth of San Joaquin River, Calif. 



THE OCEAN 



113 



of the tidal marshes along the New Jersey coast are caused by 
the scour of the tides, which is the erosion produced by the 
inrushing waters during the rising high tide and the outflow- 
ing waters during ebb tide. 

134. Ocean Currents. — The principal movement of the 
water in both waves and tides is a vertical one or an up-and- 
down motion. Yet both these agencies under certain con- 
ditions produce horizontal movements which are called currents. 




Fig. 57. — Ocean currents. The solid lines are warm currents ; the dotted 
lines are cold currents. Sargasso seas in each of the eddies. 



The water carried on the shore by the breaking waves flows 
seaward along the bottom, forming a ground current called the 
undertow. Where the waves move on the shore at an angle less 
than a right angle, a movement is started more or less parallel 
with the shore, called a shore current. Tidal races are tidal 
currents in straits or among islands. 

Besides such more or less local currents, there are wide- 
spread movements involving immense masses of ocean waters, 
forming large ocean currents which occur in all the oceans. 
The movements of warm waters into areas of colder water 



114 ELEMENTS OF PHYSICAL GEOGRAPHY 

form warm currents, and are generally toward the poles ; cold 
waters moving into warm water areas form cold currents, 
generally flowing towards the equator (Fig. 57) . 

The most extensive ocean currents are those forming five 
great eddies in the North Atlantic, South Atlantic, North 
Pacific, South Pacific, and Indian Oceans. The more quiet 
central areas of these eddies are called sargasso seas and are 
in part covered with floating vegetation, made up in large part 
of Sargassum. The main lines of travel on the oceans avoid 
the sargassos as far as possible, as the drift material impedes 
the speed of the vessels. When Columbus in his first voyage 
entered the North Atlantic Sargasso Sea the sailors were 
greatly frightened, fearing they might never escape. 

There is a smaller eddy in the North Atlantic, south of Greenland, 
and one in the North Pacific, south of Alaska. There are varied 
currents throughout Oceanica west of the South Pacific eddy, and 
varying currents in the North Indian Ocean caused in part by the 
monsoons. 

A cold current flows southwest along the east coast of the northern 
part of North America, a similar one on the east coast of northern 
Asia, and north-flowing cold currents flow along the west coasts of 
Africa and South America. 

Thus the west side of the northern oceans and the east side of the 
southern are. characterized by cold currents, and the east side of 
the northern oceans and the west side of the southern by warm 
currents. 

135. Cause of Ocean Currents. — The principal cause of 
the larger ocean currents is the wind. Since the trade winds 
are the steadiest winds in one direction they are the most im- 
portant in forming ocean currents. The direction of the currents 
is in many places influenced by the contour of the continents 
and also by deflection due to the rotation of the earth, the latter 
causing a bending to the right in the northern hemisphere and 
to the left in the southern hemisphere, following Ferrel's law 
of the winds. 



THE OCEAN 115 

136. The Gulf Stream. — The more rapid portion of the 
North Atlantic current, where it emerges from the Gulf of 
Mexico, is known as the Gulf Stream. Where it spreads out, 
covering a wide area in the North Atlantic, it is called drift, a 
name commonly applied where the movement of a current is 
slow. A still slower movement is called creep. There appears 
to be a creep of the cold waters from the Polar Seas towards 
the equator along the bottom of the ocean, as indicated by 
the lower temperature of the deep ocean waters in tropical 
seas. 

Where the polar current meets the Gulf Stream in the North At- 
lantic the warmer waters overflow the colder ones. The meeting place 
of the cold and warm currents is characterized by heavy fogs. A 
similar condition prevails off the east coast of Asia, where the warm 
and cold currents meet. 

137. Effects of Ocean Currents and Drift. — (1) The move- 
ment into higher latitudes of large bodies of warm water like 
the Gulf Stream and the Japan current carries tropical heat 
into the cold regions and tempers the climate. Compare the 
warm climate of Western Europe and the west coast of North 
America with that of Labrador and eastern Asia in the same 
latitudes. Compare also the temperature of the east and west 
coasts of South America. The effects are most pronounced 
on the west coasts of the continents, not only because the 
warm waters are brought nearer those shores, but in the high 
latitudes the prevailing winds are from the west and it is the 
air blowing over the warm waters that carries the heat to the 
land. 

(2) Ocean currents affect navigation by hastening or re- 
tarding the speed of vessels, depending upon whether they are 
going with or against the current. The lines of ocean travel 
are deflected from straight courses to take advantage of favor- 
able currents and avoid adverse ones. The direction and 
velocity of movements of the water in a current are scarcely 



116 ELEMENTS OF PHYSICAL GEOGRAPHY 

perceptible from a vessel in the current, so precautions are 
necessary to prevent vessels from drifting from their courses 
on to the rocks along dangerous coasts. Hence mariners must 
keep posted on the movements of ocean currents. 

(3) Ocean currents distribute plant life and occasionally 
animal life. The islands of the sea receive seeds which have 
drifted from other islands or the mainland. Many verdure- 
clad islands that otherwise would have remained barren have 
received their vegetation in this way. The shifting of the 
Gulf Stream eastward into deeper waters off the east coast of 
the United States some years ago is thought to have caused 
the death of millions of tile fish, which could not live in the 
colder waters that took its place. 

(4) The transfer of water by currents from one part of the 
ocean to another prevents stagnation and distributes food and 
oxygen to the life in the waters. By carrying the sewage and 
other impurities from harbors to distant parts of the sea they 
serve a twofold purpose of purifying the harbor and feeding, 
the fish. 

(5) Where cold surface currents meet warmer ones, dense 
fogs result, which are a menace to navigation. The trans- 
atlantic line of steamers between Europe and North America 
crosses such a fog area in the region of the banks southeast of 
Newfoundland. The fog is the cause of collisions between 
steamers, between the steamships and fishing vessels, and 
between ships and icebergs. It was in this fog belt that the 
Titanic collided with an iceberg in 1912, causing the loss of 
the vessel and the fives of more than 1500 people. 

138. Temperature of the Ocean. - — The surface of the ocean 
is heated by the sun's rays, but these probably do not produce 
any perceptible effect below a few hundred feet. Since water, 
like air, grows lighter as it is heated, the surface-heated waters 
do not sink, and hence heat does not reach the ocean bottom 
or any great depth in the ocean. The surface water in the 



THE OCEAN 



117 



equatorial region is heated to about 80° F. At the poles it is 
frozen part of the year and near the freezing point most of the 
time. Since the colder water becomes heavier and sinks, all 
the water of the polar oceans is near 28° F., the freezing point 
of salt water. As there is a slow creep of this water along the 
ocean bottom towards the equator, the deeper portions of 
the ocean, even in the equatorial regions, are very cold. Speci- 
mens of ooze and mud brought from the ocean bottom in the 
tropics show temperatures at or near the freezing point. 

The body of the ocean water has a rather uniform tempera- 
ture. Even the surface waters change but little in comparison 
with the land temperatures, the daily change of the surface 
rarely exceeding two or three degrees and the yearly maximum 
range being fifteen degrees. 

Soundings of the Challenger in the Atlantic Ocean, 3f degrees south 
of the equator, show the following temperatures : 

Surface 78° F. 

270 feet deep 68° F. 

960 feet deep 50° F. 

1,920 feet deep 41° F. 

9,000 feet deep 36.5° F. 

15,200 feet deep 33° F. 



CARIBBEAN SEA 

70-80*" 



ATLANTIC OCEAN 

70-80° 




75° 


MEDITERRANEAN S 


OCEAN 


70 


55 






.54 


&> 






54 


55 


^^inmft^^ 




38 


55 






37 


55 


^^2,000 ft-^^^^^^y^ 


^£^ 


35 



Fig. 58. • — Diagram illustrating relative temperatures in a mediterranean 
sea, compared with corresponding depths in the ocean basin. 



118 ELEMENTS OF PHYSICAL GEOGRAPHY 

The temperature of inland seas or mediterraneans is higher than 
that of the bordering ocean at corresponding depths, because they 
have no circulation with the polar waters, owing to the shallowness of the 
connecting strait, and hence the temperature at the bottom is never 
lower than at the lowest place in the strait connecting them with the 
open sea, or the coldest water formed in the winter season of the area. 
(See Fig. 58.) Deep waters in mediterraneans in cold regions are 
cold, but in warm regions the deep waters are warm. 

139. Density of Sea Water. — The density of sea water 
varies with the temperature, composition, and pressure. There 
is an increase in density with decrease in temperature to near 
the freezing point, where it suddenly expands and becomes 
lighter as it freezes. The average density of sea water at the 
surface at a temperature of 60° F. is about 1.06. There is a 
slight increase in density towards the bottom, due to pressure 
of "the overlying water. An increased percentage of salts in 
solution causes an increase in density. 

LIFE IN THE OCEAN 

140. Life in the Ocean. — Life in the ocean is quite varied 
and in places very prolific. The varying physical conditions 
produce three rather distinct life regions : (1) the continental 
shelf or shallow water area, (2) the bottom of the deep sea 
basins, (3) the region of pelagic life, on the surface of the open 
sea. 

141. Life on the Shore and in the Shallow Seas. — The life 
of the shallow seas includes the greater part of the more fa- 
miliar forms, such as the fishes, mollusks, crabs, lobsters, corals, 
sea urchins, starfishes, squids, and devil fish, all in great number 
and variety. In places there is also prolific vegetable life, 
which is necessary for the support of the animal life. The 
shallower portions of the ocean, known as banks, such as the 
Grand Banks off the coast of Newfoundland, are frequented by 
vessels from distant lands for the cod, halibut, and other fish 



THE OCEAN 119 

which swarm here in great numbers. Coral reefs, which grow 
only in shallow water, teem with multitudes of living forms. 
Indeed there are few places where life is more prolific than on a 
coral reef. The littoral or shore life includes the eel grass, 
marsh grass, mangrove, and other plants, besides a great 
variety of animal life (Figs. 59, 60, and 61). 




Fig. 59. — Right whale porpoise. (Photo by U. S. Fish Commission.) 

142. Deep-Sea Life. — The life on the deep ocean bottom 
is quite meager, consisting of a few strange and fantastic forms. 
The conditions are unfavorable for abundance of life, as it is 
everywhere dark, cold — almost at the freezing point — and there 
is enormous pressure from the great depth of water. 

Despite the dreary, monotonous, and unfavorable conditions 
of the deep-sea bottom, there is a growth, scanty it is true, of 
living forms over a considerable portion of it. There is probably 





;.Jb&* ■W'^^**-— , 


ajj^ ** 




§ 


' " A 




\ 




1 





Fig. 60. — Giant squid, Port Otway, Patagonia. It frequents the 
shallow waters near shore in cold climates. 

120 



THE OCEAN 



121 



no vegetation, as that requires some sunlight, and hence the 
animals of the deep-sea bottom are dependent for their food 
supply on the remains of the surface forms which sink to the 
bottom. 




Fig. 61. — Two, of the larger animals of the open sea. The upper one is a 
grampus, a small whale allied to the blackfish. The lower is a bottle-nosed 
dolphin. 



Many of the deep-sea forms, as they are brought up in dredges, 
perish as •soon as they reach the surface, because of the great change in 
pressure. At a depth of 20,000 feet there is a pressure from the over- 



122 



ELEMENTS OF PHYSICAL GEOGRAPHY 



lying water of over 600 tons per square foot. The animals of the deep 
sea resist this pressure in the same way that we resist the pressure of 
the atmosphere, namely, by having a corresponding pressure on the 
inside. When they are somewhat suddenly released from the great 
external pressure, before there is proper adjustment of the internal 
pressure, the result is generally disastrous (Fig. 62). 




Fig. 62. — One of the odd-shaped forms of life from the deep sea. 
white spots emit a phosphorescent light. (Smithsonian Report.) 



The 



143. Pelagic Life. — The life on and near the surface of the 
open sea — the pelagic life — is nearly everywhere abundant, 
but especially so in the tropical regions. There is a great 
variety as well as quantity of forms, varying in size from the 
multitudes of microscopic plants and animals (See Sec. 124) 
to huge whales. 

The floating vegetation of the sargasso seas attracts many 
forms of animal life which make it their feeding ground, and 
they in turn form food for carnivorous forms which are thus 
attracted. 

The different forms of pelagic life, including the floating vegeta- 
tion, the microscopic animals, whales, fishes, and other free-swimming 
forms, are common also in the surface waters of the shallow water areas 



THE OCEAN 



123 



of the continental shelf. The range of the different species over the 
surface of the ocean is limited by changes in temperature and not by 
the depth of the water. 

The great part of the pelagic life lies on or close to the surface of 
the ocean, between which and the sparsely inhabited sea bottom is 
the great bulk of the oceanic waters — dark, cold, dreary, monotonous 
zones — great desert areas, almost barren of life. 




Fig. 



63. — Humpback salmon, one of the food fishes of the sea that runs 
into fresh water to spawn. (Photo by U. S. Fish Commission.) 



144. Economic Features of the Ocean. — " Old Ocean's gray 
and melancholy waste," like many other poetical expressions, 
is very misleading and untrue if we attempt to apply it literally. 
It is the greatest and by far the best of all our highways, which, 
besides being free, extends to nearly every nation and serves 
to unite the civilized countries into a great commercial family. 

The ocean makes the land habitable by furnishing moisture 
and tempering the climate. It carries the warmth of the 
tropical sun to the temperate and polar regions and in turn 



124 ELEMENTS OF PHYSICAL GEOGRAPHY 

transports the cold of the poles towards the equator. It is 
the chief factor in the circulation of moisture through the 
atmosphere. 

An important part of the food supply of the world comes from 
the ocean. Probably most important of all are the fishes of 
many kinds. Make a list of the names of all the fishes that 
you know are taken from the ocean for food. Besides the 
fishes there are oysters, clams, lobsters, crabs, shrimps, walruses, 
polar bears, whales, porpoises, and seals. Other important prod- 
ucts are pearls, coral, sponges, shells, seaweed, and salt. In some 
countries seaweed is used extensively for food. In some places 
it is used as a source of potash and iodine. It is estimated 
that the annual value of the food products taken from the sea 
is not less than $500,000,000. (Fig. 63.) 

During the great World War (1914^-1918) the German submarine 
boats destroyed so many fishing vessels as to cause a marked decrease 
in the quantity of fish taken from European waters during that period ; 
but the increased demand for food during the war caused a great in- 
crease in the quantity and value of fish taken from the ocean waters 
bordering the United States and Canada. 



QUESTIONS 

1. Why is the surface of the ocean more nearly level than the land 
surface ? Why is it not perfectly level ? 

2. Name the divisions of the ocean in the order of size. 

3. Is there any significance in the fact that London, the metropolis 
of the world, is the center of the land hemisphere? 

4. Much, probably most, of the salts of the ocean were carried 
in by the rivers. Why then is there such a large percentage of sodium 
chloride and magnesium salts in the ocean and such a large percentage 
of calcium carbonate in river waters ? 

5. Why is the ocean bottom more regular and even than land 
areas ? 

6. What is the evidence that the rocks in central New York, 
Illinois, and Iowa were formed in the sea? 



THE OCEAN 125 

7. What evidence can you cite that part of the continental shelf 
east of the United States was formerly land area ? 

8. How does the movement of water in waves with whitecaps 
differ from that in waves without whitecaps ? 

9. Why do vessels in a stormy sea sometimes pour oil on the water ? 

10. Why is a boat in the open sea safer in time of storm than one 
near a shore, where there is no harbor? 

11. What different names are given to tidal waves in rivers? 

12. Why is more air mixed with the water in the breakers than in 
the smooth waves? 

13. How many high tides and how many spring tides may occur in 
the month of July ? 

14. Why do ocean vessels leaving shallow harbors not have a 
fixed schedule like a railway train? 

15. What is meant by establishing the port f 

16. Why are the high tides 12 hours and 26 minutes apart ? Why 
not just 12 hours? 

17. Suppose the moon were twice as far away as it is, what difference 
would there be in the tides? 

18. Why is there more vegetation on the surface of a sargasso sea 
than elsewhere ? 

19. What would become of a vessel if it were abandoned at the 
eastern margin of the Gulf Stream? 

20. How does the water of the deep ocean in the tropics reach a 
temperature below 40° F., when the temperature at the surface does 
not faU below 70°? 

21. Why is the water on the bottom of the ocean a little denser 
than at the top ? 

22. Many fish and other animals of the ocean bottom are phos- 
phorescent. What advantages, what disadvantages does this property 
give the animal? 

23. During the European war (1914-1918) the fisheries of the United 
States increased in value, those of England and Germany decreased. 
Why? 

24. Why is seasickness more likely to occur on small boats than on 
large ones ? In the ground swell at the margin of storms than in the 
storm ? 

25. Do salt lakes freeze? Explain. 



CHAPTER IV 

SHORE LINES AND COAST FEATURES 

The line where land and water areas meet is called a shore 
line. It is the boundary line of continents, islands, oceans, 
and lakes. The coast is a strip of land bordering the shore. 
The beach is the area between high and low water on a sloping 
coast ; where the shore line is on a vertical cliff there is no 
beach. 

Shore lines are seldom stationary or fixed through long 
periods of time such as successive periods in geologic history. 
A depression of the land causes an advance of the shore line 
inland, and hence a larger sea area. An elevation of the land 
causes a recession of the shore line and a larger land area. 
During such an advance or recession the shore line must pass 
over every portion of the area between the old and new shore 
lines. If the recession is caused by a succession of uplifts, at 
the end of each stage where the shore line remains stationary 
for a period of time, beaches and other characteristic features, 
such as those described in the following pages, are formed to 
mark the location of such a period. A geographer who is 
familiar with the varied shore features is able to recognize old 
or former shore lines by similar marks on the land surface or 
even in the bed rocks. It was in this way that Mr. Gilbert 
worked out the past history of Great Salt Lake, which is but 
a remnant of the former greater Lake Bonneville. 1 

1 Lake Bonneville, by G. K. Gilbert, Monograph I of the United States 
Geological Survey. In this admirable monograph the reader will find one of 
the oldest and in some respects one of the best descriptions of typical shore 
features, as well as a charming history of the former lake. 

126 



SHORE LINES AND COAST FEATURES 127 

It has been found that shore lines undergo regular and sys- 
tematic changes, as do rivers, mountains, and other natural 
features, so that the geographer reads the past history and 
forecasts future changes, while studying present shore features. 

145. Shore Erosion. — The rocks along the shore are sub- 
ject to erosion, intense in some places, and slight in others. 




Fig. 64. — Shore lines in miniature ; made by subsidence of the water. 
(Photo by U. S. Geological Survey.) 

The waves furnish the energy or force, and the sand, gravel, 
and boulders of the beach are the tools used by the wave energy 
to grind away the hard rocks. Where there is no beach and 
the rock cliff extends down below the water level, the waves 
beat against the face of the cliff, producing almost no erosion 
(Fig. 64). 

The weathering agents, such as heat, cold, frost, wind, chemical 
action, plants, and animals, aid in breaking up the massive rock into 
fragments, but it is the energy of the waves that bumps these frag- 



128 



ELEMENTS OF PHYSICAL GEOGRAPHY 



ments together and hurls them against the bed rock, grinding all to 
sand and mud, which are carried back by the undertow. Most of the 
erosion is done by storm waves. The tides assist the waves by lifting 
and lowering them to other points of attack (Fig. 65). 




Fig. 65. — Wave erosion on a rocky shore, California coast, showing sea 
caves and natural bridges. (Photo by J. C. Branner.) 

146. Effect of Storm Waves. — The eroding work of storm 
waves on a coast is confined largely to a vertical range from 
about 50 feet below low tide to 100 feet or more above high 
tide. Along this zone their force is frequently terrific. Their 
work is accomplished in several ways : 

(1) The impact of the boulders, shingle, and sand, that are 
picked up by the waves and hurled against the rocks with great 
force, loosens more material from the cliff and breaks and 
grinds up that already loosened. On the Bahama Islands, 
blocks weighing 20 tons have been hurled by the waves 125 
feet from the shore and 25 feet above high water (Fig. 66). 

(2) The boulders, gravel, and sand torn from the cliff are 
rolled up and down the sloping beach, being thus worn smaller, 
while the finer material is swept back into deeper water. 



SHORE LINES AND COAST FEATURES 



129 



(3) The spray acts both mechanically and chemically. On the 
coast of Scotland, lighthouse windows have been broken by the spray 
at the height of 300 feet. The spray dashing against the rocks, high 




Fig. 66. — Wave erosion on the Maryland coast. Erosion by the waves 
has here uncovered an old buried cypress forest. The remains of both the an- 
cient forest and the living one are being buried in the sands of the beach to tell 
the story in future ages. (Photo by Maryland Geological Survey.) 



above the reach of the waves, assists in the chemical disintegration of 
the rock constituents (Fig. 67) . 

(4) The hydrostatic pressure of the water, and the compression 
and expansion of the air driven by the waves into the crevices and 
caves along the shore, are agents of disintegration. 

Tidal Waves. — True tidal waves are not very powerful 
eroding agents on the open seashore, but in bays, estuaries, 
and river channels they are often active. The bore or pororoca 
of the Amazon, the mascaret of the Seine, and similar waves 



130 ELEMENTS OF PHYSICAL GEOGRAPHY 

in other rivers, are great tidal waves which sweep with high 
velocity up the river channel, destroying and tearing away the 
material along the banks, proving destructive to boats on the 
river as well as to property on the shore. The so-called tidal 
wave that destroyed so much property and flooded such ex- 
tensive land areas at Galveston in 1902, produced by the 
hurricane which it accompanied, was in no way related to the 
tide, but was an unusually great storm wave. 

147. Earthquake Waves. — Sometimes a coast or a portion of a 
coast is visited by a large and very destructive wave, frequently 
called a tidal wave, but wrongly so, as in nearly all cases it accompanies 
an earthquake or volcanic disturbance. Such waves are not destructive 
on the open sea, where they pass as low waves of great length often 
unperceived ; but as they approach the shore the water begins to 
pile, up and rush in on the shore in an overwhelming flood that causes 
enormous loss of life and property, and frequently changes the shore line 
beyond recognition. Destructive earthquake waves have their origin 
beneath the ocean ; earthquakes that originate on land, as the San 
Francisco earthquake in 1906, do not produce destructive waves. 

148. Transportation and Deposition Along the Shore. — The 

volume of water that is carried in on the shore on the crest of 
the waves, is returned along the bottom in the undertow which 
carries back with it the fine material formed by the grinding 
of the shingle on the beach. This material is carried out from 
the beach and deposited in the order of the size of the frag- 
ments, with the coarse near the shore and the finest farthest 
out. Where there are currents at or near the shore, they affect 
the distribution of the material by moving it along the beach 
or carrying it farther out in the sea. Besides that carried out 
by the undertow there is frequently a movement of material 
along the beach by the waves and the shore currents produced 
by the waves where they strike the shore obliquely. It is in 
this way that bars, cusps, spits, hooks, and wall beaches are 
formed. 



SHORE LINES AND COAST FEATURES 



131 




Fig. 67. 



Wave-eroded shore cliff in horizontal rocks composed of hard 
and soft layers. (Photo by Van Wormer.) 



132 



ELEMENTS OF PHYSICAL GEOGRAPHY 



149. Topographic and Structural Features of Shore Lines. — 

Where the waves beat against a rocky shore, they cut away 
the rocks near the water line, and the shore line moves land- 




Fig. 68. — Wave-eroded shore cliff, showing chimney rocks and shingle beach 
composed of wave-worn fragments. Soldier's Cove, Bay of Fundy, N. S. 

ward by the wearing away of the rocks, forming the wave-cut 
terrace. As the terrace is cut back into higher land the latter 
is undermined, and a vertical or overhanging shore cliff is formed, 




Fig. 69. — Wave-cut and wave-built terrace formed by wave erosion. 

which continues to break down because of repeated under- 
cutting of the upper portion ; this, as it falls down, is ground 
up and carried away. (See Figs. 67, 68, 69, and 70.) 



SHORE LINES AND COAST FEATURES 



133 



The material ground up by the waves at the base of the cliff 
is carried back into deeper water by the undertow and de- 
posited beyond the edge of the wave-cut terrace, making the 
wave-built terrace. Successive terraces, or a series of terraces 
resembling steps, result from interrupted elevations of the 
bordering land, while the waves are forming the terraces. 
Such a succession of terraces occurs along the California Coast 
(See Fig. 70), and on the north side of Lake Superior and Lake 




Fig. 70. 



Wave-cut rock terrace on the California coast. 



Ontario. Similar terraces on the slopes around Great Salt 
Lake have been formed by periodic sinkings of the lake level 
and corresponding shore lines of the earlier Lake Bonneville. 
(See Figs. 64 and 259.) 

Chimney Rocks. — - As the waves and the gravel beach cut 
into the rock cliff, some portions of it are left standing, while 
the waves cut down and carry away the material on all sides. 
These remnants commonly include portions between joint- 
planes and are generally for that reason quite angular, sometimes 
rectangular. From their form they are called chimney rocks or 
stacks. (See Figs. 68, 71, and 72.) 



134 



ELEMENTS OF PHYSICAL GEOGRAPHY 



150. Effect of Dikes on the Shore Line. — Sometimes a dike of 
igneous rock is more resistant to the weather than the surrounding 
rock, which, crumbling away more rapidly, leaves the dike standing 
above the surface, often like a great row of eordwood, jutting out 
on the beach, sometimes even out into the water. In other places 
the igneous dike weathers more rapidly than the surrounding rock, 




Fig. 71. 



Chimney rock and sea cave, Perce Rock, N. S. 
S. Power.) 



(Photo by 



and thus forms a great chasm extending back into the cliff where the 
dike material has been torn out by the waves. Sometimes a chasm 
of this kind is cut across a headland, separating it from the mainland, 
thus forming an island. There is one place on the north shore of Lake 
Superior where from a boat one may see fourteen of these dark-colored 
dikes cutting the light-colored granite rock within a distance of less 
than a mile. 



151. Sea Caves. — Sea caves are formed when the waves 
undercut the cliff more rapidly at one point (Figs. 65 and 71). 
They commonly begin at a soft place in the rock, a fissure, or a 



SHORE LIXES AXD COAST FEATURES 



135 



joint-plane. Generally such caves are not very long, because 
as soon as the opening is made, the inrushing wave blocks the 




Fig. 72. — Chimney rock at Portland on the coast of England. 

mouth of- the cave, when the air is compressed and acts as a 
cushion to protect the rocks within from the force of the wave. 



136 



ELEMENTS OF PHYSICAL GEOGRAPHY 



The compression of the air and its sudden expansion when the 
wave recedes may tear loose some blocks and thus enlarge the 
cave. Sometimes the land side of the cave is worn away, 
leaving a natural bridge on the shore. (See Figs. 65 and 71.) 

Whistling caves and blow holes are formed in the sea eaves, where 
an opening oeeurs in the roof that permits the escape of the imprisoned 




Fig. 73. — Spouting cave formed in the ice on shore of Lake Ontario. Some- 
what similar caves are formed in the rocks by the waves. (Photo by M. S. 
Lovell.) 



air, which rushes out, often with great violence, producing a noise 
something like a steam whistle. Sometimes these caves are so shaped 
that not only the air, but a column of water, is forced out through 
the opening at the top, forming the spouting cave (Fig. 73). 

152. The Beach. — The beach varies in character at different 
points. In the smaller coves on the headlands and on the bold, 
rocky shores, there are great accumulations of boulders and 
gravel. (See Fig. 68.) At the head of the larger bays and 



SHORE LINES AND COAST FEATURES 



137 



along low shores the beach is covered with sand or mud. The 
character of the material on the beach largely depends upon 
whether there is a shore cliff, the kind of rock in the cliff, the 
shape of the cliff, the form of the shore adjoiniDg the cliff, and 
the direction of the winds. 




Fig. 74. — Shell beach on the shore of one of the islands in the Pacific Ocean. 
(Photo by U. S. Fish Commission.) 



The shingle beaches are formed at the base of rock cliffs 
where the fragments from the cliff are ground up by the waves 
(Fig. 68). Where the incoming waves strike the shingle beach 
obliquely, the material is moved along the beach beyond 
the end of the cliff, forming the wall beach or traveling beach, 
which sometimes extends across the mouth of a stream and 
forms a lake, or causes the stream to shift its course beyond 



138 



ELEMENTS OF PHYSICAL GEOGRAPHY 



the end of the wall beach. The shingle beach is formed where- 
ever material is eroded from the cliff faster than it is carried 
back into deep water. A shell beach is formed by the 
waves washing up myriads of shells from the bordering sea 
(Fig. 74). 

153. Spit, Hook, Cusp. — Winds and shore currents transfer 
materials along the beach, and frequently, where there is a 




Fig. 75. 



Dutch Point, Lake Michigan. A hooked sandspit. 
by U. S. Geological Survey.) 



(Photo 



bend in the shore, the shore current, continuing its direction, 
carries the beach accumulation out from the shore as a point 
or arm, which is known as a spit. When the point is curved 
sharply it forms a hook, or hooked spit (Fig. 75). The curving 
of the hook is commonly due to the action of another current 
at an angle to the first one. The second current may be tem- 
porary, due to a violent storm ; and after it ceases, the spit 
may continue in the direction first taken until it meets another 
storm, where another hook may form, making in this way a 



SHORE LINES AND COAST FEATURES 139 

series of hooks or barbs on the same spit (Fig. 75). Spits 
are also formed in quiet waters between two currents which 
carry sediment. 

Cusps are pointed projections from the shore which are much 
smaller than spits. They commonly occur at more or less 
regular intervals along a curving sandy beach and are generally 
temporary features, destroyed by the next storm. 




Fig. 76. — Bay bar formed by meeting of two sandspits at Fair Haven, N. Y. 
(Photo by the author.) 

154. Bars. — A spit formed at a headland at the opening 
of a bay, or along the sides of a bay, will in time, if it is not 
checked by a strong river or tidal current through the bay, 
extend entirely across,' joining the land on the opposite side, 
thus forming a bar, sometimes called a bay bar to distinguish 
it from bars formed in other ways. Where bars form across 
the mouth of a bay they form a new shore line and straighten 
the shore at that point (Fig. 76) . 



140 



ELEMENTS OF PHYSICAL GEOGRAPHY 



Islands, if they occur in shallow water near the shore, where 
there is sufficient deposition, are joined or tied to the shore by 




Fig. 77. — Tie-bars connecting the island of Monte Argentario with the 
mainland of Italy. 

bars, called tie-bars, which start as a spit from the island or 
the mainland or both. There may be one or two or more tie- 
bars tying the island to the shore (Fig. 77). 



SHORE LINES AND COAST FEATURES 



141 



155. Barriers. — Where there is a stretch of shallow water 
off shore, there is sometimes a violent agitation of the bottom 
sand and mud by waves, which form the breakers at some 
distance out from the shore. The meeting in these muddy 
waters of the waves from the sea on one side and the undertow 
from the land on the other side checks the velocity of each, 




Fig. 78. 



Barrier beach and spit on shore of Lake Champlain. 
by H. M. Brock.) 



(Photo 



causes a deposit, and builds up an off-shore ridge or bar, which 
in time reaches the surface, above which it is built by the waves 
and wind. Such an off-shore bar is called a barrier. The 
shallow water or lagoon behind the barrier is in time filled up 
by the sediment carried in by the rivers, the sand and dust 
carried by the winds, both aided materially by the accumulations 
of vegetable and animal matter. After the filling of the lagoon, 
the former barrier becomes the beach of the new shore line 
and another barrier develops, in this way extending the land 
area into the sea. A barrier beach is formed where the water 



142 



ELEMENTS OF PHYSICAL GEOGRAPHY 




is s 



5 w> 



SHORE LINES AND COAST FEATURES 



143 




144 



ELEMENTS OF PHYSICAL GEOGRAPHY 



is too shallow for the waves to attack the shore (Fig. 78). (For 
description of the coral barrier reef see Sec. 161.) 

156. Irregular Shore Lines. — Shore lines that are very- 
irregular are generally formed by the sinking of a hilly land 
area, causing a landward advance of the shore line, in which 
case the sea extends up the valleys, forming bays, estuaries, 




Fig. 81. — Regular and irregular shore line formed by wave erosion and 
deposition. The material is diatomaceous earth. (Photo by Maryland 
Geological Survey.) 

and fiords, and the hills form headlands, capes, peninsulas, 
and islands. The peaks of partially submerged hills form 
islands along the new coast. The work of the waves on such 
a shore is apt at first to intensify the irregularities and make 
new ones, owing to the fact that the more rapid erosion of the 
softer rocks makes additional bays. After a time, however, 
bars form across the bays, they begin to fill up, erosion is con- 
centrated on the headlands, both processes tending to straighten 
the shore line. (See Figs. 50, 65, and 71, and Plate II and other 
contour maps of the Maine coast.) 

157. Regular Shore Lines. — Regular shore lines are formed 
(1) by the uplift of the land causing the shore line to move 



PLATE II 




Part of Boolhbay, Me., Sheet, U. S. Geological Survey. 

Irregular Shore Line Due to Submergence of the Land and Advance 
of the Sea on a Hilly Region. 



PLATE III 




Part of Navesinlt, N. J., Sheet, U. S. Geological Survey. 

Regular Shore Line on Recently Uplifted Land Area Further 
Straightened by Wave Work. 



SHORE LINES AND COAST FEATURES 



145 



seaward on to the newly uplifted coastal plain ; or (2) by the 
waves eroding the headlands, and waves and shore currents 
building bars across the bays, and the filling up of the bays 
(Figs. 79, 80, and 81), or (3) the building of sand barrier reefs 
parallel to the shore, causing a movement of the shore outward 
to the barrier, and the later filling in of the lagoons and marshes 
behind the barrier (Plate III). 



SHORE LINES MODIFIED BY LIVING FORMS 

A shore line is sometimes greatly modified by accumulations 
of organic matter, both vegetable and animal. 

158. Shore Lines Modified by Vegetation. — In tropical 
regions one of the most important plants that affect the shore 




- Mangrove trees at low tide. Shore of Gilbert Island, Pacific 
Ocean. (Photo by U. S. Fish Commission.) 

line is the mangrove tree, one of the very few trees that flourish 
in salt water. The seed often sprouts while still attached to 
the branch, and sends forth a long radicle or stem which ex- 
tends to the mud at the bottom and takes root, a new trunk 



146 



ELEMENTS OF PHYSICAL GEOGRAPHY 



being formed from the top of the root. From the trunk many 
spreading roots extend to the sea bottom, and many branches 
form at the top, some extending downward to start new roots 
and new trunks, until a single parent tree is surrounded by a 
small grove. Some of the fruit drops off and floats away on 




Fig. 83. — Mangrove trees at Jupiter Inlet, coast of Florida. 

the water with the long radicle extending downward until 
it finally becomes attached to the bottom mud and starts a 
new tree and a new grove. This network of roots catches and 
holds drift material and mud, until a solid embankment is 
built up. The shallow lagoon between it and the mainland 
in time fills with accumulated vegetable and animal matter and 
mud deposits. A continuation of this process extends the 
shore line seaward wherever the building up is faster than the 
destruction by the waves. The shore plain built in this way 



SHORE LINES AND COAST FEATURES 



147 



is apt to be wet and marshy. The mangrove is very abundant 
on the coast of Florida, and on many islands in the Pacific 
Ocean (Figs. 82, 83). 




Fig. 84. 



Colony of living coral. (Photo of drawing from Smithsonian 
Report.) 



Eel and Marsh Grass. — The mangrove does not grow north 
of Florida, but the low-lying plains bordering the shallow water along 
the northern shore of the United States are extended seaward in places 
in a somewhat similar manner by another kind of vegetation. The 



148 ELEMENTS OF PHYSICAL GEOGRAPHY 

eel grass grows over the shallow bottom below low tide, where it acts 
as a trap to catch the mud stirred up by the waves, until the bottom 
is raised to low- tide level, when the marsh grass takes possession and 
aids in the upbuilding process up to or sometimes above high-tide 
level. The repetition of this process causes the extension of the eel 
and marsh grass plains seaward. 



Fig. 85. — Coral head in Makiano atoll, Pacific Ocean. (Photo by U. S. 
Fish Commission.) 

159. Coral. — One of the most prominent of all the land 
builders along the shores is the coral polyp, an animal that 
secretes carbonate of lime, which it extracts from sea water. 
It grows in such multitudes that even though a single coral 
polyp secretes but a small quantity of lime, the aggregate is 
something astounding. The Great Barrier Reef off the coast 
of Australia is more than 1000 miles long and contains a mass 



SHORE LINES AND COAST FEATURES 



149 



of limestone probably equal to any of the great limestone beds 
extending through the central and eastern United States. 

The reef-building coral nourishes only in tropical seas, where 
the winter temperature of the waters does not fall below 68° F. 
It does not grow above the surface of the salt water at low tide, 
because it cannot live out of water, nor at depths much greater 
than one hundred feet. It does not grow in muddy waters, 
hence is not found at the mouths of rivers. It grows best in 
waters that are violently agitated by the waves and currents, 
hence it is not found in great abundance inside the atolls, but 
flourishes on the outside in the midst of the surf and breakers. 
The reason for this is that it needs a constant supply of food, 
oxygen and carbonate of lime, which is soon exhausted in the 
lagoon, but is constantly renewed by the moving waters in the 
breakers (Figs. 84 and 85). 

160. Thick Coral Beds. — While the coral does not grow at 
depths greater than 100 feet, some of the reefs appear to be several 




Fig. 86. — Illustrating the development of an atoll from a fringing coral 
reef. FF, a fringing reef when the sea level was at SS. S'S', level of the sea 
after sinking of the island ; BB, barrier reef. A A, coral atoll surrounding lagoon 
after further sinking of the island. S"S", present sea level. 



thousand feet deep; at least the dredge brings up dead coral from 
that depth off the shore of the reefs. This is accounted for in two 
ways : (1) The coral growing outward from the reef at the top forms 
overhanging masses which break off from their weight or are broken 



150 



ELEMENTS OF PHYSICAL GEOGRAPHY 



off by the waves and slide down the steeply inclined sea bottom into 
deep water ; or (2) the bottom subsides as the coral is growing and the 
coral that grows near the surface is carried down into deep waters by 
the sinking of the bottom. This may continue indefinitely without 
killing the coral at the top, providing the sinking does not take place 
more rapidly than the coral grows. The sinking may be slower, but 
not faster (Fig. 86). 

161. Coral Reefs. — The coral deposits attached to the 
shore form fringing reefs, such as those on the Bahama Islands. 




Fig. 87. 



Part of Pinaki coral atoll and barrier reef. 
(Photo by U. S. Fish Commission.) 



Pacific Ocean. 



Those that occur out from the shore at distances varying from 
a fraction of a mile to several miles, form barrier reefs, such as the 
keys off the coast of Florida. Such reefs are separated from 
the mainland by a lagoon, which is frequently deep enough 
for a ship channel. 

By subsidence of the island a fringing reef may become a 
barrier reef and in time an atoll, or circular reef, inclosing a 
body of salt water, or lagoon. Atolls may also be formed by 



SHORE LINES AND COAST FEATURES 



151 



coral growth on the rim of an extinct volcano or on any sea 

bottom less than 100 feet deep. Whitsunday, Caroline, and 

many other islands in the Pacific are atolls (Figs. 87 and 88). 

Other explanations of the origin of atolls have been offered. 




Fig. 8b. — Part of a coral reef. Pacific Ocean. (Photo by U. S. Fish 
Commission.) 

162. Fossil Reefs. — There are fossil coral reefs in the limestone 
beds at Syracuse, New York, at the falls of the Ohio River at Louis- 
ville, Kentucky, at Chicago, Illinois, and at many other places in the 
United States, signifying that these areas were at one time covered 
by the sea, with conditions favorable to coral growth. What does 
this indicate regarding the climate of central and northern United 
States in times past? 



163. Limestone from Plants and Animals Other than Coral. — 

Growing in the same waters with the corals, is a great variety 
of other animals and plants, many of which secrete carbonate 
of lime, while others deposit silica. Such are the different 



152 ELEMENTS OF PHYSICAL GEOGRAPHY 

kinds of mollusks, crinoids, and sponges. There are also many 
microscopic forms. The aggregate remains of the multitude 
of different forms are mingled with the corals in the formation 
of the coral limestone beds. In many places extensive beds of 




Fig. 89. — Fossil shell limestone, Chazy, N. Y., formed ages ago in the mar- 
gin of the sea that then surrounded the Adirondack Mountains. (Photo by 
H. M. Brock.) 

limestone or siliceous rock are formed by the mollusks and other 
forms of life, without any reef-building coral (Figs. 74 and 
89). The coquina limestone now forming in this way along 
the Florida coast is used to some extent for building stone. 
164. Lake Shores. — Lake shore lines are similar to ocean 
shore lines in many ways. The lake waves are neither so large 
nor so strong as the ocean waves, hence the erosion is not so 
rapid. The water, except that in the salt lakes, is not so dense, 
hence sediment is not carried as freely as in salt waters. In the 
northern latitudes the lakes, except a few of the largest ones, 
freeze over in the winter season, and are not subject to active 



SHORE LINES AND COAST FEATURES 153 

erosion on the shore by the winter winds. The ice, while pro- 
tecting the shore from the winds, becomes an active agent of 
erosion in itself. The expansion of the ice due to changes in 
temperature causes it to push against the shore with great 
force. When the frozen surface is broken up by warm weather 
the blocks are driven on the shore by storm winds. 

There is no coral in fresh water, and most of the other forms of life 
common in the ocean do not occur in the lakes, which have a fauna 
and flora of their own. In the larger lakes the Irving forms affect 
the shore line very little ; but in small lakes, vegetation accumulates 
along the shore and forms marshy plains which in time cover the whole 
lake basin. Some of the small lakes are bordered by plains composed 
of marl, which consists of the remains of animals and plants that grew 
in the lake in quantities sufficient to fill it partly and sometimes en- 
tirely. (See Chapter X.) 

165. Fossil Shore Lines. — How may we recognize a former 
shore line after the body of water which caused it has dis- 
appeared? Many of the features explained on the preceding 
pages are characteristic of shores and not found elsewhere ; 
hence a recognition of these features means a recognition of a 
former shore line. 

North of Lake Superior, at different elevations on the hills, 
are boulder beaches similar to those at the water's edge today. 
At other points are the wave-built sand terraces, similar to 
those forming on the present shore. These old beaches are at 
different elevations above the lake, some less than one hundred, 
some more than three hundred feet above the water. (See 
Fig. 259.) 

Along the coast of California in several places are wave-cut 
terraces many feet above the sea, indicating a recent elevation 
of the land that carried the former shore line high above the 
sea level (Fig. 70). 

Besides the beaches, wave-cut rock, and wave-built sand 
terraces, other shore features that may often be recognized 



154 



ELEMENTS OF PHYSICAL GEOGRAPHY 



on extinct lakes are wave-cut cliffs, bars, spits, hooks, and 
deltas. 

Examples. Surrounding Great Salt Lake, in places some miles 
from the lake, is a prominent shore line, or rather a series of them, 
indicating the levels of a former great lake which has been called Lake 




Fig. 90. — Part of boulder beach formed on the shore of glacial Lake Iroquois 
at Corey Hill, Canada, formed during the Glacial Period, now 480 feet above 
sea level. (Photo by H. M. Brock.) 

Bonneville. Lake Agassiz in central North America, Lake Passaic in 
New Jersey, and Lake Iroquois in New York are other fossil lakes 
which have been recognized and located by their shore lines. (See 
Fig. 90.) 

SAND DUNES 

166. Formation. — Sand dunes are common features on sandy 
coast regions, especially so where the prevailing winds are from 
the sea. The sand washed on the beach in high water becomes 
dry during low water and is blown along the surface by the 
winds, building up ridges called dunes. The ridge once formed 



SHORE LINES AND COAST FEATURES 



155 



moves in the direction of the wind, frequently growing larger 
as it moves. The movement is caused by the sand on the 
surface of the windward slope being carried by the wind over 
the crest, where it is deposited on the lee slope (Fig. 91). 



Fig. 




Sand dunes showin 



wind ripples 
Survey.) 



(Photo by U. S. Geological 



In regions of strong prevailing winds the dune ridges some- 
times move for miles, covering and destroying much property 
on the way, farms, buildings, even forests (Fig. 92). In an 
area of variable winds the dunes are modified in form and 
direction of movement with every change in wind, generally 
forming a mass of low irregular hills. 

167. Occurrence of Sand Dunes. — Sand dunes occur along 
all sandy portions of the Pacific Coast, where they are moved 
inland by the prevailing westerly winds. But since the Coast 
Mountains lie close to or extend into the sea, the sandy coastal 



156 



ELEMENTS OF PHYSICAL GEOGRAPHY 



areas are small. Along the Atlantic and Gulf Coasts of the 
United States there are extensive areas of sand, but the pre- 
vailing westerly winds blow the sand into the sea. On some 
portions of the Atlantic Coast the onshore winds are sufficiently 




Fig. 92. — Advancing sand dune burying a forest at Dune Park, Ind. 
(Photo by H. C. Cowles.) 

strong and continuous to form dune areas, especially so on the 
projecting points, such as Cape Hatteras, Cape Henry, and 
Cape Cod. Small sand dunes fcr m on most of the sand barriers 
bordering the coast. 



Dunes of large size form on the east and southeast coast bordering 
Lake Michigan. In places they have been carried over productive 
farm lands and in other places over forests. Similar but smaller dunes 
occur at the east end of Lake Ontario in New York (Figs. 92 and 93). 

It is only in humid regions that sand dunes are largely confined 
to coastal areas. In arid and semi-arid regions, where there are long 
dry seasons, in which the vegetation dies and bare soil areas are ex- 



SHORE LINES AND COAST FEATURES 157 

posed to the winds, sand dunes are common features. Dunes are 
even more characteristic of deserts than they are of shore lines. 

Throughout the lower portion of the Basin region between the 
Rocky Mountains and the Sierra Nevadas are extensive dune areas. 
Smaller dune areas occur in places over the plateaus. Many dune 
areas occur on the Great Western Plains along the courses of the 




Fig. 93. — Advancing sand dune at Dune Park, Ind. (Photo by H. C. 

Cowles.) 

Missouri, Platte, Arkansas, and Canadian Rivers, formed by the 
sand blown from the river beds in dry seasons. These are more 
common on the south side of these rivers, showing that the strongest 
winds in these areas are north winds. One of the largest sand-dune 
areas in the United States is the " Sand Hill Region" of northwestern 
Nebraska, but most of these sand hills are dead dunes, now covered 
with vegetation and no longer moving (Fig. 94). 

On a small map of the United States indicate the sand-dune areas, 
and compare the map with one showing the swamp and marsh areas. 

168. Protection from Dunes. — Several plans have been 
used with more or less success to check moving sand dunes 
from advancing upon and destroying productive lands. The 
erection of a barrier as shown in Fig. 95 proves helpful where 



158 ELEMENTS OF PHYSICAL GEOGRAPHY 

the dunes have not yet formed. Where a large dune is ad- 
vancing as shown in Fig. 92 a remedy is found in constructing 
a board or brush barrier on the crest of the dune, and elevating 
the barrier or constructing another before the first is entirely 




Fig. 94. — Sand dunes held by growing vegetation. Sand plains of the Rio 
Grande, near Brownsville, Tex. (Photo by W. L. Bray.) 

covered, thus causing the dune to build up on the crest until 
it reaches such a height that the winds cannot carry sand over 
the crest. Nature has formed such a barrier dune at Selkirk, 
on the east shore of Lake Ontario. 

The most efficient plan is to cover the sand area with forest 
growth, which makes it a productive instead of a destructive 
area. Where the winds are strong it is difficult to start forest 



SHORE LINES AND COAST FEATURES 



159 



growth because the moving sand destroys the young trees. In 
this case the area should be planted with dune grass, a plant 




Fig. 95. — Diagram showing method of checking drifting sand. A solid 
barrier, A, causes a dune in front of it. An open but rigid barrier, B, causes the 
dune to form in and finally over it. An open flexible barrier, C, causes the dune 
to form behind. The sand moves from left to right in the diagram. (After 
the U. S. Department of Agriculture.) 

which grows at the top while the bottom is being covered with 
sand. This serves to check the sand enough to allow the forest 
trees to get a start. 



160 ELEMENTS OF PHYSICAL GEOGRAPHY 

A large area on the west coast of France has been changed in this way 
from a barren waste to a productive forest area, which furnished some 
of the lumber so much needed during the great World War. Small 
areas in different parts of the United States have been reclaimed in 
a similar manner. 



HARBORS AND SEAPORTS 

169. Harbors and Seaports. — The most important economic 
features of sea coasts are harbors suitable for ports. A sea- 
port is a place where goods are loaded and unloaded from vessels 
engaged in commerce. A harbor is a place of shelter for vessels 
in time of storm. Most seaports are located on good harbors 
as a matter of economy. Occasionally ports are established 
at points on the coast where there is no harbor. Nome City 
on the Alaskan coast is an example. Large quantities of gold 
were found in the sands and gravels of the beach and bordering 
coastal regions. People came to get the gold, and a city grew 
up. Food, clothing, building materials, everything needed 
in a city had to be shipped in. The only highway was the 
ocean, but there was no harbor ; ships could not get close to 
shore because of shallow water. They have no protection in 
time of storm. Freight and passengers are unloaded by lighter- 
ing, that is, a lighter vessel or small boat takes part of the cargo 
to the shore. Sometimes horses and cattle are thrown from 
the vessels and made to swim ashore. In time of storm un- 
loading is stopped and the vessel, to prevent destruction in 
the breakers, must go out to sea and wait until the storm sub- 
sides. This makes the loading and unloading of vessels slow 
and expensive. 

170. Artificial Harbors. — Where the traffic is sufficient to 
justify the expense, an artificial harbor is made if there is no 
natural harbor available. San Diego and Los Angeles are two 
cities in southern California. The former has a fine harbor, 
but the country inland from the city is mountainous and arid 



SHORE LINES AND COAST FEATURES 



161 



and will not support a large population. Los Angeles, sup- 
ported by a very productive and prosperous surrounding farm- 
ing region, had no good harbor. To remedy this defect the 




Point Fermin L.H. 



Fig. 96. — Los Angeles Harbor at San Pedro, Calif., showing position of the 
breakwater built to protect the shipping in the harbor from the ocean waves. 



United States Government made an artificial one by building 
a great breakwater, out in the ocean, behind which is the harbor 
of San Pedro, the port for Los Angeles. (See Fig. 96 and 
contour maps of San Diego and Los Angeles.) 

Study the Oswego Sheet of the United States Topographic Atlas 
and see how Oswego has twice enlarged its harbor to accommodate 
the growing traffic on Lake Ontario (Fig. 97). It is now considering 
a third enlargement. Study contour maps of Erie, Pennsylvania, 
San Francisco, and Boston. 



162 



ELEMENTS OF PHYSICAL GEOGRAPHY 



An artificial harbor is sometimes made by making a basin 
on the land, large enough for a harbor, and connecting it with 
the sea or lake by a canal. This was done at Gary, Indiana, 
on the sandy coast of Lake Michigan. 1 




Fig. 97. 



View showing the lighthouse and part of the breakwater at Oswego 
Harbor, Lake Ontario. (Photo by the author.) 



Manchester, England, became a seaport by the construction of 
a ship canal 35 miles long from the city to the sea. Amsterdam, 
Holland, and Houston, Texas, became seaports in the same 
way. 

171. Conditions for a Good Harbor. — The conditions for 
a good harbor are : (1) protection from incoming heavy waves ; 
(2) an open deep channel extending from the anchorage to 
the sea ; (3) water deep enough to permit the vessels to ap- 

1 See the chapter on Gary, Indiana, in the Representative Cities of the United 
States, by C. W. Hotchkiss. 



SHORE LINES AND COAST FEATURES 163 

proach close to the shore line to facilitate loading and unload- 
ing ; (4) room enough to accommodate many vessels without 
interference ; (5) good bottom for anchorage ; (6) absence of 
strong river or tidal currents. Moreover, (7) in order that 
the harbor may become a great seaport there must be easy 
access into a productive interior country capable of supporting 
a large population, and (8) fresh water is desirable, as it kills 
the barnacles that are attached to the ship in salt water. Seattle, 
Washington, at considerable expense constructed a canal from 
Puget Sound into Lake Washington in the city and now has 
both a salt-water and a fresh-water harbor. The citizens of 
Seattle have shown much enterprise in improving their natural 
advantages until it now has the largest commerce of any sea- 
port on the Pacific Coast. 

172. Kinds of Harbors. — (1) Delta harbors, on the delta of a great 
river, have the advantage of access by water to the great fertile plains 
of the interior of the continent, but they are often hampered by the 
difficulty of keeping a ship channel open and free from the mass of 
mud carried in by the river. New Orleans is on the Mississippi Delta. 

(2) Bay and estuary delta harbors are on drowned rivers where the 
sea has entered the lower part of the valley and a new delta has been 
formed at the head of the bay or estuary. Frequently a sand bar or 
spit forms at the entrance to the bay and protects the shipping from 
storm waves. (See Fig. 98.) 

(3) Fiord harbors differ from the preceding in being deeper, and 
generally lying in rock depressions with less soil on the bordering hills 
than commonly occurs along the bays or estuaries. The fiords represent 
the deep ice-worn channels of glacial origin, and hence are found 
only in high latitudes where glaciers at some time have extended into 
the sea. Their origin accounts for the bare rock walls and scarcity 
of mantle rock. They are abundant on the coast of Norway (Fig. 99). 
Others occur on the coast of Maine. 

(4) Mountain ranges that project into the sea frequently have 
troughs or depressions below sea level which may be utilized as harbors. 
Such is the western end of the Pyrenees in Spain, and the peninsula 
and islands of Greece. Sometimes the mountains are parallel to the 
coast, and the harbor or harbors may he inside the first range, as San 



164 ELEMENTS OF PHYSICAL GEOGRAPHY 

Francisco Bay and many similar land-locked areas along the coast of 
Washington and Alaska. 

(5) Glacial moraine deposits along a sea coast sometimes form pro- 
tected harbors. 



U.S.GEOLOGICAL SURVEY. 




THIRTEENTH ANNUAL REPORT. PL. XXII 






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Fig. 98. — Mobile Bay and Harbor. Harbor protected by sandspits. 



SHORE LINES AND COAST FEATURES 



165 



(6) Lagoon and sand-bar harbors occur on almost all sandy shores 
where there is a long stretch of shallow sea bordering the coast. The 
waves build up a barrier at some distance off shore, and the lagoon be- 
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for the modern ocean steamship, unless deepened artificially by dredg- 
ing, but they serve a useful purpose for the smaller coasting vessels. 

(7) Sandspit harbors are similar in some respects to the last men- 
tioned, but in the spit the sand is drifted along the shore until in 
drifting past the headland at the entrance of the bay the spit is carried 
part way or perhaps entirely across the bay, thus forming a safe 
anchorage in the bay behind it. Provincetown, on Cape Cod, is an 
example of this class (Fig. 98). 

(8) Volcanic crater harbors are formed by a breach in the rim of 
a volcanic crater that occurs near sea level, on an island or the border 
of a continent. The accompanying view (Fig. 100) shows such a 
crater at the village of Ischia, on the island of Ischia, near Naples. 



166 



ELEMENTS OF PHYSICAL GEOGRAPHY 



The notch in the rim of the crater permits small vessels to enter and 
find a snug harbor in the crater of the extinct volcano. 

(9) Coral reefs and atolls furnish many much-needed harbors in 
the tropics. The lagoon inside of the barrier reef or on the interior 
of an atoll frequently furnishes a good harbor for large as well as small 




Fig. 100. 



Volcanic crater harbor on the island 
(Photo by the author.) 



of Ischia, near Naples. 



vessels. Often the entrance to the coral harbor is narrow, intricate, 
and dangerous. Biscayne Bay, on the east coast of Florida, is an 
example of a coral barrier-reef harbor ; and Hamilton, on the Ber- 
mudas, is an example of an atoll harbor. Both of these types are 
much more numerous in the Pacific than in the Atlantic Ocean. 



173. Economic Importance of Harbors. — The presence or 
absence of good harbors has much to do with the location of 
cities and the commercial prosperity of the adjacent region. 
The location of San Francisco is not an accident. It has one 
of the best harbors on the Pacific coast, which is at the same 



SHORE LINES AND COAST FEATURES 167 

time a connecting link between the ocean and the great fertile 
interior valley of California. New York City, on the east 
coast, is the metropolis of the United States mainly because 
of its good harbor, located at the natural doorway into the 
interior of the continent through the Hudson and Mohawk 
Valleys and the Great Lakes. Boston, Philadelphia, Balti- 
more, Washington, and all the prominent cities on the eastern 
coast owe their locations to their good harbors. 

ISLANDS 

174. Islands. — Many islands are intimately related to the 
continents and form an important part of the history of the 
coast. All islands may be grouped into two classes : (1) con- 
tinental islands, those which occur on the continental shelf, 
in proximity to the shores of the continent, and (2) oceanic 
islands, those which rise out of the ocean basins. 

Continental islands are either tops of hills whose bases have 
been covered by the advancing sea on a subsiding coast, or 
elevations built up on the continental shelf until they extend 
above sea level. The first are generally composed of hard 
rock, bordered, at least in part, by rocky cliffs and sometimes 
reaching considerable elevation above the sea, such as the 
islands along the Maine coast and many of those along the 
Pacific coast. 

Some of the built-up islands are sand barriers or remnants 
of such, like those along the Gulf coast and the Atlantic coast 
south of New York, others are coral reefs or atolls built up by 
coral, others are volcanoes built up on the shallow sea bottom 
of the continental shelf, some are formed by mangrove trees. 

They are in general comparatively new features and will 
soon be either destroyed by the waves beating on the shores 
of the islands, or they will be joined to the mainland of the 
continent. 



168 ELEMENTS OF PHYSICAL GEOGRAPHY 

Islands vary in size from a few square feet to hundreds of 
square miles in area. They differ from continents not only 
in size, but in conformation : islands generally slope from the 
interior to the sea, while the interior of the continents consists 
largely of lowlands, great river or interior basins separated 
from the sea by mountain ranges. From this standpoint 
Australia is a continent ; possibly Antarctica and Greenland 
are also, but since the greater part of both the latter is mostly 
covered with glaciers little is known of their interior. 



QUESTIONS 

1. Explain how waves erode the rocks on the shore line. 

2. Why is a cliff with a beach at its base eroded more rapidly 
than one without a beach? 

3. What finally becomes of the pebbles and boulders on a rocky 
beach ? 

4. Where a series of terraces occurs at successively higher levels 
above the present beach, which is older, the highest or the lowest 
terrace ? 

5. How may a whistling cave change to a spouting cave and then 
to a natural bridge ? 

6. Are spits more common on an old shore line or a young shore 
line? 

7. Explain how rock islands and sand islands along a coast differ 
in origin. 

8. Which of the two kinds of islands should you expect on an ad- 
vancing shore fine ? Which on a receding shore line ? Which occurs on 
the Maine coast ? Which on the New Jersey coast ? 

9. Describe the southwest coast of Florida, where mangrove trees 
grow. 

10. The old shore of extinct Lake Iroquois is about 400 feet higher 
east of Lake Ontario than it is at the west end. How do you explain 
the difference? 

11. Why are there more and larger sand dunes on the east side of 
Lake Michigan than on the west side? 

12. Why are sand dunes more frequent in arid regions than in humid 
regions ? 



SHORE LINES AND COAST FEATURES 169 

13. How can living or moving sand dunes be killed or made sta- 
tionary? Why are most of the dunes of the "Sand Hill Region" of 
Nebraska dead? 

14. In what respects is a fresh- water harbor better than a salt- 
water one? 

15. What are the geographic reasons why New York City is the 
metropolis of the United States? 



CHAPTER V 
THE LAND 

MINEKALS AND ROCKS 

175. Composition of the Earth's Crust. — In the chemical 
laboratory, water can be separated into two gases called oxygen 
and hydrogen. If these gases are placed together in the same 
tube, they will not reunite to form water until heat is applied. 
Put a lighted match into the mixture of the two gases and they 
unite so suddenly as to cause a violent explosion. The gases 
have again combined into a chemical union forming water. 

The separate gases, oxygen and hydrogen, are called elements 
because they cannot be subdivided into simpler substances. 
The chemical union of the two is called a compound. 

The entire mass of the earth, the atmosphere, the water, 
and the solid or land portion, is made up of elements and com- 
pounds formed of elements. 

Some of the elements, when free from compounds, at ordinary 
temperature are gases, such as oxygen, hydrogen, and nitrogen ; 
some are liquid, as mercury ; some are solid, as iron, copper, gold, 
etc. The same thing is true of the compounds formed from 
the elements. Some are gases, as carbonic acid gas, a com- 
pound of carbon and oxygen ; some are liquid, as water and 
oil ; some are solid, as limestone, a compound of carbonic acid 
and lime. 

Both the elements and the compounds change condition with change 
in temperature. Thus, with sufficient increase in temperature solids 
change to liquids or even gases. Decrease the temperature and gases 
change to liquids and then to solids. Thus, lower the temperature 

170 



THE LAND 171 

of water to 32° F. and it freezes into solid ice, raise the temperature 
to 212° F. and it changes to a gas, water vapor. It requires different 
temperatures to change the condition of different substances. Rocks 
like granite if melted would freeze solid at a temperature above a 
thousand degrees, while oxygen and nitrogen require a lowering of the 
temperature nearly to absolute zero (—460° F.) before they freeze. 

The land is the part of the earth that is solid at ordinary 
temperatures, but even this is subject to variation. In the 
polar regions much of the water is solid through a large part 
of the year. In the volcanoes large quantities of rock material 
are temporarily liquid, some of it even gaseous for a time. If 
the molten lava cools quickly it forms glass. If it cools slowly 
the elements in the lava combine into definite compounds 
called minerals. 

Elements and their compounds in solution in water or acids, 
under certain conditions separate from the solution as solids 
called minerals. 

176. Minerals. — Minerals are chemical elements or com- 
pounds produced by inorganic agencies. Most minerals have 
separated from solutions or from lavas, which are simply solu- 
tions at high temperatures. A mineral may consist of a single 
element, such as native gold or copper, or carbon in the form of 
graphite or diamond ; but most of the minerals are chemical 
compounds like quartz, composed of two elements, silicon 
and oxygen ; or pyrite, a compound of iron and sulphur. 
Some of them are very complex compounds of several ele- 
ments, such as hornblende, which contains calcium, aluminum, 
silicon, sodium, magnesium, two chemical forms of iron, and 
oxygen. 

Chemists have discovered so far about eighty different ele- 
ments ; mineralogists have distinguished hundreds of minerals 
in the rocks of the earth ; petrologists have determined a 
great many kinds of rocks made up of different aggregates of 
minerals. 



172 



ELEMENTS OF PHYSICAL GEOGRAPHY 



It would seem at first glance like a hopeless task for a be- 
ginning student to learn much about minerals and rocks of the 
earth in a short time when there are so many. But hopeless 
may be changed to hopeful on learning that more than 99 per 
cent of the known part of the earth is made up of eight of the 
eighty elements, combined in a dozen or two mineral aggre- 
gates, called rocks. 

It is the chemist and not the geographer that studies the rare ele- 
ments. It is the mineralogist that is interested in the hundreds of 
minerals other than the few common ones. It is the petrologist that 
is interested in the rare varieties of rocks. The student needs the 
knowledge of only a few of the common elements, common minerals, 
and common rocks to know enough about the land to study geography. 

177. The Commonest Chemical Elements. — The eight 
elements forming most of the known part of the earth are 




MaS ■ £ 
Potassium I . /» 
All others not \../* 



Fig. 101. — Diagram illustrating the approximate percentage of the most com- 
mon elements forming the known part of the earth. (Hessler and Smith.) 



oxygen, silicon, aluminum, iron, calcium, magnesium, sodium, 
and potassium. A number of the other elements are common 
and fairly abundant, such as nitrogen, which forms four-fifths 
of the atmosphere ; hydrogen, which forms one-ninth of the 



THE LAND 173 

water ; carbon, which forms a large part of the coal, petroleum, 
and limestone ; and such metals as gold, silver, copper, lead, 
zinc, etc. If carbon, sulphur, chlorine, and phosphorus were 
added to the eight named, the list would include about all the 
elements of the common rock-forming minerals (Fig. 101). 

178. Properties of Minerals. — Minerals are distinguished 
from each other by their different physical and chemical proper- 
ties. The principal physical properties considered are hard- 
ness, tenacity, cleavage, fracture, luster, color, crystal form 
and habit, and optical, electrical, and magnetic properties. 
The composition is determined by chemical analysis, most 
commonly with the use of a blowpipe and certain chemical 
reagents. 

Minerals may be classified into groups based on the chemical com- 
position, or on the crystal form and habit, or for commercial purposes 
on their industrial uses. 

In noting the hardness of minerals it is customary to select 
a certain number, generally ten, and arrange them in order of 
relative hardness, as a scale of comparison. The ones commonly 
selected are (1) talc, (2) gypsum, (3) calcite, (4) fluorite, (5) apa- 
tite, (6) orthoclase, (7) quartz, (8) topaz, (9) corundum, (10) di- 
amond. By comparing any other mineral with these, its hard- 
ness can be designated by a number corresponding to that given 
to the mineral with which it agrees in the scale. For example, 
a mineral that would scratch calcite, but not fluorite, would 
be marked 4 in the scale, commonly written H. 4 or H = 4. 

179. Forms of Crystals. - — All crystal forms may be divided 
into six groups or systems, but the determination of these in- 
volves more knowledge of crystallography than can be given 
here. Compare the crystals as to the number of faces, and the 
arrangement of them. The different kinds and degrees of 
cleavage and luster can be learned by a comparison of the 
different minerals (Fig. 102). 





1. Cube 

Galena, Halite, 

Pyrite. 



2. Pyritohedron. 
Pyrite. 




3. Octohedron. 

Magnetite, Pyrite, 

Fluorite. 





Hexagonal. 
4. Prism and Pyramid, 5. 
Quartz. 





6*. Scalenohedron.' 
Quartz Crystal. Calcite-Dog-tooth-Spar. 





<y 




7. Rhombobedron. 8. Monoclinic. 9. Trapezohedron. 

Cleavage form of Calcite. Orthoclase Feldspar. Garnet. 

Fig. 102. — Some of the common crystal forms. The same mineral may 
occur in different forms, but always in the same system. Thus pyrite in the 
isometric system may occur in any one of the first three forms. 

174 



THE LAND 



175 



Color is an important aid in distinguishing minerals, despite the 
fact that some minerals have a great variety of colors. The streak 
or fine powder of some minerals has a different color from a larger 
piece, as is shown by rubbing the mineral on unglazed porcelain, or 
scratching it with a file. The color of the streak of minerals harder 
than porcelain may be obtained by crushing a fragment with a hammer. 

A careful study of the different properties will in most cases en- 
able one to determine any unknown mineral. To learn to do this one 
must study and handle specimens of minerals. It cannot be learned 
from descriptions. 

The following pages contain a brief description of the most abundant 
minerals, which should be studied along with the specimens until they 
are familiar. If the mineral specimens are not available for study, the 
following pages, descriptive of minerals, should be omitted. 

Rock-forming Minerals. - — The most important rock-form- 
ing minerals are quartz, the feldspars, micas, hornblende, 
augite, olivine, calcite, dolomite, serpentine, and kaolin. 

180. Quartz. — Quartz, the oxide of silicon (Si0 2 ), forms 
one of the essential minerals in granite, the bulk of the grains 




Fig. 103. — A cluster of quartz crystals. 



176 ELEMENTS OF PHYSICAL GEOGRAPHY 

in most of the sandstones, and a part of some other rocks. It 
is one of the hardest of the common minerals, 7 in the scale, 
readily scratching glass. It crystallizes in six-sided prisms 
with pyramids (Fig. 103). It has a conchoidal fracture, no 
cleavage, and commonly a vitreous luster, some varieties hav- 
ing a waxy luster and others a dull luster. It occurs in nearly 
all the different colors, but in the granites and sandstones 
it is usually gray, white, or colorless. The streak, difficult to 
obtain, is white or gray. In the mineral form it is used com- 
mercially in the manufacture of glass and porcelain. Some 
varieties, as rock crystal, amethyst, jasper, and chrysoprase, 
are used as gems. Some sandpaper is made from ground 
quartz. Compare quartz with calcite, feldspar, fluorite, and 
gypsum. 

181. Feldspars. — These are divided into two classes, 
orthoclase and plagioclase. The first prevails in granites and 
syenites, the other in dio rites and gabbros." Orthoclase con- 
tains potash (K 2 0) combined with silica (Si0 2 ) and alumina 
(A1 2 3 ), while 'plagioclase contains soda (Na>0) or lime (CaO) 
or both in place of the potash. The feldspars are not quite 
so hard as quartz, being one less in the scale, but are still hard 
enough to scratch glass. They differ from quartz in having 
bright cleavage surfaces in two directions at right angles or 
nearly so. Feldspar becomes dull on weathering as it dis- 
integrates and finally crumbles into a soft, clayey mass. Feld- 
spar is commonly white, gray, or pink in color. It is quarried 
in New York, Pennsylvania, New Hampshire, and elsewhere, 
and is used in the manufacture of porcelain and chinaware. 
(See Figs. 102 and 104.) 

182. Micas. — Micas are characterized by the extremely 
thin plates or scales into which they may be separated, due to 
perfect cleavage. There are several different varieties, of which 
muscovite and biotite are the most common. Muscovite, the 
so-called isinglass, is colorless in thin pieces when pure. It is 



THE LAND 



177 



used for electrical purposes, lanterns, stove and furnace doors, 
as a lubricant, and for decorative purposes. It occurs in granite, 
syenite, and some schists. Muscovite has a composition 
somewhat similar to that of orthoclase. Biotite, the black 




Fig. 



104. A feldspar quarry in Chester Co., Penna., where the feldspar is 
quarried for commercial use. (Photo by the author.) 



mica, contains iron oxide and magnesia in addition to the potash 
of the muscovite. It occurs in many igneous rocks. 

183. Hornblende.* — Hornblende, the most common of the 
amphiboles, is a black mineral occurring in syenite, diorite, 
some granites, and schists. It may be distinguished from 
biotite by its not separating in thin scales. While black is the 
most common color in hornblende, some varieties have other 
colors. 

184. Augite. — Augite, the most common of the pyroxenes, 
is a dark green, nearly black, mineral which occurs in diabase, 



178 



ELEMENTS OF PHYSICAL GEOGRAPHY 



basalt, gabbro, and other rocks. Augite and hornblende are 
important rock-making minerals, composed of silicates of iron, 
magnesia, and lime. Varieties of each differ in color, but if 
they form a large part of the rock mass, the augite is very 
dark green and the hornblende is black. The augite is com- 
monly in thick short crystals or irregular masses, hornblende 
usually in long, slender crystals, sometimes finely fibrous. 

Olivine is a brighter green than augite, commonly granular or mas- 
sive, and occurs most frequently in dark-colored igneous rocks. 

185. Calcite. — Calcite is composed of the carbonate of 
calcium (CaC0 3 ) and forms the bulk of the limestones, marbles, 




Fig. 105. — Travertine, calcite deposited by springs, quarried for building 
stone at Cave Barco, near Rome. (Photo by J. C. Branner.) 

and chalk deposits. It forms a large part of many marls and 
of shells of all kinds, most of the coral, extensive deposits in 
caves and about lime springs (See Fig. 105), and occurs in veins 



THE LAND 



179 



or fissures in different kinds of rocks. The limestones and 
marbles, besides having extensive use as building and orna- 
mental stone, are used for making quicklime and cement, and 
hence they form the base of most of the mortars in building 




Fig. 106. — Travertine deposit in fossil Lake Lahontan basin, Nev. 
(Photo by C. Van Duyne.) 



operations. Calcite is one of the most useful of all the minerals 
and fortunately is very widely distributed. Compare calcite 
with dolomite, quartz, feldspar, and fluorite, and point out the 
differences, telling how you would distinguish them. When 
pure it is colorless to white ; impure varieties occur in all 
colors — red, black, blue, gray, and yellow being abundant. 
It cleaves readily in three directions into rhombohedrons. 
Clear forms, Iceland spar, show double refraction. It effer- 
vesces freely in dilute acids. In cavities in the rocks it fre- 
quently crystallizes in sharp pointed crystals, known as dog-tooth 
spar. (See Fig. 102.) 

186. Dolomite. — Dolomite is the double carbonate of 
lime and magnesia (CaC0 3 , MgCOs), and hence differs from 



180 ELEMENTS OF PHYSICAL GEOGRAPHY 

calcite in having part of the lime replaced by magnesia. It 
frequently resembles calcite so closely, especially in many 
limestones and marbles, that it is difficult to distinguish one 
from the other. They may commonly be distinguished by 
adding quite dilute cold hydrochloric acid, in which the calcite 
will effervesce vigorously and the dolomite but little, if at all, 
until the acid is heated. 

187. Kaolin or Kaolinite. — When pure, kaolin is white and 
forms china clay. It is formed by the decomposition of feld- 
spars, micas, etc., by the action of the groundwater leaching 
out the potash, soda, and lime, leaving the insoluble silicate 
of alumina, which combined with water forms kaolin (A1 2 3 , 
2 Si02, 2 H 2 0). It is used in the manufacture of china and 
porcelain ware, encaustic tile, and as a filler for paper. Mixed 
with other materials it probably forms the bulk of all the clays 
and shales, and a considerable portion of most of the soils. 

OEES 

Ores are the minerals from which metals are obtained. A 
few of the metals, such as gold and copper, occur in the metallic 
state in nature ; but most generally the metals in nature are 
combined with one or more other elements, forming compounds 
known as ores. The metals usually combine with oxygen, 
forming oxides ; sulphur, forming sulphides ; or carbonic acid, 
forming carbonates. 

Some minerals, such as feldspars, micas, hornblende, etc., contain 
metals but are not ores. Only the metal-bearing minerals from which 
the metal is or can be extracted commercially are called ores. 

188. Iron Ores. — Iron, the most useful of all the metals, 
occurs in nature in all three of the above compounds in its 
different ores. 

Hematite (red hematite, fossil ore, specular ore) is at present 
the most important ore of iron in the United States, and from 



THE LAND 



181 



it more than four-fifths of our iron is manufactured. It occurs 
in several varieties, some of a bright red color, some steel gray, 
and some almost black. Whatever the color of the mass, the 
streak or powder is always red. Hematite forms the body of 
red paints. In nature it gives the color to red soils and red 




Fig. 107. — Map of the United States showing distribution of iron ores. The 
Lake Superior district and Alabama are the two most productive areas. 



rocks. Hematite consists of ferric oxide (Fe 2 3 ), the higher 
oxide of iron. The most productive locality for this ore is the 
region about Lake Superior, from which much of the ore is 
shipped by boats on the Great Lakes. It is mined extensively 
in Alabama, and in smaller quantities in New York, Tennessee, 
Virginia, Missouri, and other states (Fig. 107). 

Lrimonite (brown hematite, bog ore, yellow ochre), the hydrous 
ferric oxide (2 Fe 2 3 , 3 H 2 0), differs in composition from 
hematite by having water combined with the iron oxide. It 
has the same composition as the rust that forms on iron ob- 
jects exposed to the air. It varies in color from yellow ochre to 



182 



ELEMENTS OF PHYSICAL GEOGRAPHY 



very dark brown, almost black, but the streak is always brown 
or yellow. It forms the yellow and brown coloring matter in 
nearly all the soils and mantle rock. It is deposited in bogs, 
forming the bog ore, and occurs in many places in the mantle 




Fig. 108. — View in an iron ore mine near Plattsburg, N. Y. 

author.) 



(Photo by the 



rock, especially in that resulting from decayed limestone. It 
has been mined in hundreds of places along the limestone areas 
in the Great Valley of the Appalachians and elsewhere. 

Magnetite, another oxide of iron, consists of the union of the 
ferric and ferrous, or the higher and lower iron oxides (Fe 2 3 , 
FeO), and when pure contains a higher percentage of iron than 
any of the other ores. It differs from the other oxides and 
from all other minerals by its strong magnetic properties. 
Three other minerals, one variety of hematite, the bronze- 
colored iron sulphide, pyrrhotite, and franklinite, are slightly 
magnetic, but no other minerals are attracted as strongly by a 



THE LAND 183 

magnet as magnetite. One variety of magnetite, called lode- 
stone, is not only magnetic, but is itself a magnet. Magnetite 
is black in color and the streak is black, which distinguishes 
it from the other iron ores. It occurs in the Adirondack Moun- 
tains, in southeastern New York, along the eastern part of the 
Appalachians, and elsewhere (Fig. 108). One of the largest 
magnetite mines in the United States is at Cornwall, near 
Lebanon, Pennsylvania. 

Iron pyrites is a yellow, brass-colored mineral, the sulphide of iron 
(FeS 2 ), sometimes called "fool's gold," because frequently mistaken 
for the precious metal. The name is appropriate, because despite 
the resemblance in color it may be so easily and surely distinguished 
from gold. When placed in the fire or on a hot stove, it turns black, 
gives off an odor of burning sulphur, and becomes magnetic. It is 
hard and brittle, while gold is soft and malleable. While commonly 
classed with the iron ores, pyrites are not used for the manufacture 
of iron in the United States, because the sulphur would injure the 
quality of the product. It is used for the sulphur in the manufacture 
of sulphuric acid and other products. 

Siderite, the carbonate of iron (FeC0 3 ), is formed by the combi- 
nation of carbonic acid with the oxide of iron. It varies in color from 
gray to brown and sometimes black, as in the black-band ore. It 
occurs associated with coal beds and as black nodular masses in the 
shale beds, where it forms the clay ironstone. It is used extensively 
in England for the production of iron, but is so used very little in the 
United States at present. 

189. Copper Ores. — In the Lake Superior district copper 
occurs in the metallic state, native copper, but in the western 
areas it occurs mostly in the compounds of the metal with 
carbonic acid or with sulphur, carbonates, and sulphides. 

Chalcopyrite, the most common copper ore, is a sulphide of copper 
and iron, is yellow in color, and is frequently mistaken for iron pyrite. 
It differs from iron pyrite in being softer, hence more easily scratched, 
having a more golden yellow color, and giving a blackish green color 
in the powder. Bornite, another sulphide, varies in color, being blue, 
purple, and yellow. There are two carbonates of copper — malachite, 
having a bright green color, and azurite, a deep blue, both of which 



184 ELEMENTS OF PHYSICAL GEOGRAPHY 

beside their use as a source of copper are sometimes used for orna- 
mental purposes. Other copper minerals are used for ores. 

190. Lead Ores. — The most common ore of lead is galena, 
a sulphide of lead (PbS) which looks much like the metal. It 
crystallizes in cubes, and has a cubical cleavage, that is, when 
broken it parts along planes parallel to the faces of the cube. 
Its cleavage combined with its brittleness distinguish it readily 
from the metallic lead which it resembles in color. Its color, 
cleavage, and specific gravity (6-7) distinguish it from other 
minerals. Galena frequently contains silver, and most of the 
silver mines produce large quantities of lead as a by-product. 
Some lead is obtained from cerussite, the carbonate of -lead. 

191. Zinc Ores. — The chief zinc ore is sphalerite or zinc blende, a 
sulphide of zinc (ZnS), called "jack" by the miners. It has usually a 
brown color, nearly black at times, and a resinous luster. The most 
productive localities are Missouri, Kansas, and Wisconsin. In New 
Jersey much zinc is obtained from franklinite, a bluish-black mineral 
resembling magnetite, and from zincite, a red-colored oxide of zinc. 
Willemite, a silicate of zinc, occurs with the New Jersey ores. 

192. Aluminum Ores. — Bauxite (Al .0 , 2 H 2 0), mined in 
Virginia, Alabama, and Arkansas, is practically the only ore 
of aluminum at the present time, although the metal occurs 
abundantly in many other minerals. Cryolite (A1F 3 ), formerly 
used almost entirely as a source of aluminum, was at one time 
shipped in large quantities from Greenland. Corundum 
(A1 2 3 ) is nearly pure alumina, that is, the oxide of the metal ; 
emery, ruby, and sapphire are varieties of corundum. Alumi- 
num forms a part of the clay in all the great clay and shale 
beds, but it is too difficult to separate from the silica in the clay 
to make the clay a source of the metal. 

This is only a partial list of the ores ; other important metals, the 
ores of which are mined in different places, are nickel, cobalt, manga- 
nese, tin, mercury, tungsten, molybdenum, and titanium, also the 
precious metals, gold, silver, and platinum, besides some rare metals, 
such as vanadium, osmium, iridium, etc. 



THE LAND 



185 



OTHER ECONOMIC MINERALS 

Among economic minerals other than ores, are halite, gypsum, 
sulphur, graphite, talc, magnesite, fluorite, apatite, nitre, and sylvite. 

193. Halite. — Halite (NaCl) or rock salt is mined from the 
strata deep below the surface in New York, Michigan, Ohio, 
Kansas, Louisiana, and elsewhere. It is frequently obtained 




Fig. 109. 



Scene in the salt yards at Syracuse, N. Y. (Photo by the 
author.) 



by drilling wells down to the bed of salt, running in water which 
dissolves the salt, then pumping out the water and evaporating 
it. At Syracuse, New York, the salt is already in solution by 
groundwater, so that it is only necessary to pump out the salt 
water and evaporate it. In places in Utah, Nevada, and 
southern California, salt occurs in great abundance on the 
surface, ready to be gathered up and utilized. In some lo- 
calities it is mined like coal from underground workings. In 



186 



ELEMENTS OF PHYSICAL GEOGRAPHY 



other places it is obtained by evaporating sea water. It is dis- 
tinguished from all other minerals by its taste. (See Fig. 109.) 
194. Gypsum. — Gypsum (CaS0 4 , 2 H 2 0) is the sulphate 
of lime combined with the water of crystallization, H = 2, luster, 
pearly to dull. Compare it with calcite. When heated enough 




Fig. 110. — View in a gypsum quarry, near Lyndon, N. Y. The gypsum 
is used in the manufacture of Portland cement. (Photo by the author.) 

to drive off some of the water, it forms the plaster of paris. It 
is used in making wall-plaster and stucco work, as a fertilizer 
for soil, and in the manufacture of Portland cement. Alabaster, 
a variety of gypsum, is used for ornamental purposes. Gypsum 
occurs in beds separated by layers of shale and associated with 
salt beds in many places. It is quarried in New York, Michigan, 
Kansas, Iowa, and many of the other western states. (See 
Fig. 110.) 

195. Sulphur. — Sulphur is obtained in Louisiana, Texas, 
Wyoming, Nevada, and elsewhere. Much of that used in the 



THE LAND 187 

United States was formerly imported from the island of Sicily, 
but since the beginning of the Great War in 1914 there has been 
a great increase from the mines of Louisiana, Texas, and the 
western states. Some sulphur is imported from Japan. Sul- 
phur is used for making matches, gunpowder, and sulphuric 
acid, as a disinfectant, and for other purposes. Large quan- 
tities of sulphur, used in making sulphuric acid, are obtained 
from roasting iron pyrite, the sulphide of iron. 













JL^r^ . . ft-tllkmH 




^. H 


1 > ■ *" j^lBMNii ^ff — - — - - - 


HmI^Bi& ■ 







Fig. 111. — View in a graphite mine, near Hague, N. Y. 

196. Graphite. — Graphite, sometimes called black lead, 
is a soft, black mineral composed of nearly pure carbon. 
It is mined in the Adirondack Mountains, New York, in 
Pennsylvania, and in several of the western states, but the 
best quality is imported from the island of Ceylon. It is 
used in the manufacture of lead pencils, crucibles, paint, 
and stove polish, as a lubricant, and for other purposes 
(Fig. 111). 



188 ELEMENTS OF PHYSICAL GEOGRAPHY 

197. Talc. — Talc is mined in St. Lawrence county, New 
York, in Virginia, Pennsylvania, New Hampshire, Vermont, 
North Carolina, and a few other states. It is composed of the 
hydrous silicate of magnesia, is one of the softest (H = l) of all 
the minerals, and has a characteristic greasy, soapy feel. It is 
used as a filler in paper manufacture and for toilet powder ; 
the soapstone variety is used for switchboards in electrical 
work, and for table tops in chemical laboratories ; for household 
purposes it is used for sinks, laundry tubs, cake griddles, foot 
warmers, etc. Compare specimens of soapstone with foliated 
talc, describing the differences. 

Magnesite, the carbonate of magnesia, is used in making carbonic 
acid for soda fountains, as a filler for paper, and for lining furnaces. 
It is quarried to some extent in California, but much of that used in 
the United States is imported. 

Apatite and Phosphate Rock. The phosphate of lime used 
so extensively as a fertilizer constitutes the mineral apatite. 
The purer mineral form is quarried in Canada and the more 
massive rock form is quarried in Florida, South Carolina, 
Tennessee, Alabama, and elsewhere. Extensive phosphate 
beds have been found recently in Wyoming, Idaho, and Mon- 
tana (Fig. 112). 

Fluorite is a mineral formed by the chemical union of fluorine and 
calcium (CaF 2 ). It crystallizes in cubes and octahedrons, but it cleaves 
more commonly into octahedrons ; it is generally green or purple in 
color, but is sometimes colorless. It is used as a furnace flux and for 
the manufacture of hydrofluoric acid, which etches glass. 

Nitre, sometimes called saltpeter, the nitrate of potassium (KN0 3 ), 
is used in making gunpowder, as a fertilizer, and for other purposes. 
Soda nitre or Chile saltpeter (NaN0 3 ) is now used in larger quantities 
than potassium nitre. It occurs in extensive deposits in Chile. 

Many minerals are used for gems and ornamental stones, such as 
diamond, ruby, sapphire, opal, onyx, agate, tourmaline, topaz, and 
many others. Besides the minerals mentioned above, there are a 



THE LAND 



189 



hundred or more common ones somewhat widely distributed, a number 
of them having some economic importance. There are also many 







.•^rf^gK 






jj& 


WljkJ' -iB^yl 






/ 


1 # IB '*■&& m m' 




4SM 






MSfcV^V: 


5# ' ' ' 


fc -JOSS 






■Efc^- . 


WS33B8&* 


p~.^-- . ~ 


| 


„^~; . — .,* 


hMiB^i^^P 







Fig. 112. 



Dredging phosphate rock from the river at Dunellon, Fla. 
(Photo by Geological Survey of Florida.) 



hundreds that are much less common and many of them exceedingly 
rare. Make a list of the minerals you have studied, with the char- 
acteristic properties of each. 

EOCKS 

The minerals, either singly or in various combinations, make 
up most of the rocks on the exterior of the earth. Some rocks, 
as limestone or serpentine, are composed of a single mineral, 
while others, as granite or diabase, are composed of several 
different ones. In the glassy volcanic rocks there are no separate 
minerals, although they consist probably of fused minerals 
which in the glass have lost their identity. 

Rocks are usually grouped in three general classes, based on 
origin, namely, sedimentary, igneous, and metamorphic. 




Fig. 113. — Exposed edges of a series of stratified or sedimentary rocks. 
The separate layers vary in hardness and thickness. (Photo by B. W. Clark.) 



190 



THE LAND 191 

Sedimentary Rocks 

198. Sedimentary Rocks. — Sedimentary or stratified rocks are 
formed by the accumulation of sediments in water, and therefore 
occur in layers or strata (Fig. 113). Included in this class are 
certain wind-formed deposits, which might be distinguished as 
eolian. The sedimentary rocks are divided into the following 
groups, based on the chemical composition of the rock mass : 

(1) Siliceous. Most of the sand and gravel deposits are 
siliceous and largely, sometimes entirely, composed of ground-up 
fragments of quartz. Along with the quartz grains there are 
frequently variable quantities of fragments of other common 
minerals. 

In sandstones the grains are cemented together by some 
substance, most commonly clay, iron oxide, calcite, or silica ; 
sometimes two or more of these substances may act as cement 
in the same rock. In the process of weathering of sandstones, 
the cementing substance is the first to give way; when it is 
destroyed, the sandstone crumbles to sand, from which it was 
first formed (Fig. 114). 

Conglomerate is formed much like sandstone, with pebbles 
and gravel in place of sand grains. If instead of the rounded 
pebbles of the conglomerate, the fragments are angular, like 
broken rock, and cemented together, breccia is formed. 

(2) Argillaceous. The argillaceous or clayey rocks include 
the beds of clay or mud, shale, and slate. Clay may grade 
imperceptibly into shale and this in turn through sandy shale 
into sandstones or through calcareous shale into limestone and 
by metamorphism into slate. Mud that has been deposited 
in thin layers and hardened is called shale. Some of the 
varieties of clay are china clay, brick clay, potter's clay, and 
fire clay. 

(3) Calcareous. The calcareous rocks are composed of the 
minerals calcite and dolomite, and include the many varieties 



192 



ELEMENTS OF PHYSICAL GEOGRAPHY 



of limestone and marble. Some of the common varieties of 
limestone are shell limestone ; coral limestone ; oolitic lime- 
stone ; chalk ; travertine, including the stalactites and the 




Fig. 114. — Microphotograph of a brown sandstone. The white grains 
are nearly all quartz. The black part is iron oxide (hematite), which gives the 
red or brown color to the rocks and acts as one of the cements to bind the 
grains into a solid rock. (Photo by the author.) 



stalagmites of the caves, and the tufa deposits formed about 
springs; hydraulic limestone or water lime; marl; and litho- 
graphic limestone. Gypsum, the sulphate of lime, might be 
added to the calcareous group. (See Figs. 115 and 110.) 

Limestone is used extensively for building stone, for furnace 
flux, for macadamizing highways, for ballast for railways, for 
making lime, and hydraulic and Portland cement, and as a 
fertilizer for land; at Syracuse, New York, and elsewhere it 



THE LAND 



193 



is used in large quantities in making soda ash. These and other 
uses of limestone make it one of the most important rocks of 
the earth (Fig. 115). 




Fig. 115. — Limestone quarry in one of the ridges of the Allegheny Moun- 
tains at Bellefonte, Penna. The limestone from this quarry is used for making 
quicklime. (Photo by the author.) 

(4) Carbonaceous. The carbonaceous rocks include the com- 
pounds of carbon and the hydrocarbon compounds, such as 
bituminous and anthracite coal, lignite, peat, asphalt, petroleum,, 
and natural gas (Fig. 116). 

The carbonaceous rocks are formed from accumulated masses 
of vegetable and animal remains. They do not form as much 
of the earth's crust as the sandstones, shales, and limestones, 
but they are more useful to man and are among the most 
important materials taken from the earth. With the exception 



194 



ELEMENTS OF PHYSICAL GEOGRAPHY 



of asphalt, their chief use is as fuels. Along with wood and 
water power they furnish the energy to run the factories and 
engines, and heat and light our buildings and cities. Fortu- 
nately they are rather widely distributed over the United 




Fig. 116. — The black band near the base of the bluff is an outcrop of a 
bed of coal in the bank of Powder River, Wyo. (Photo by U. S. Geological 
Survey.) 

States. Coal is produced in twenty-nine states. Pennsylvania, 
West Virginia, Illinois, Ohio, and Kentucky are the largest 
coal-producing states. Pennsylvania produces more than all 
the other states. In 1915 the coal production in the United 
States was over 531 million tons, valued at more than 686 
million dollars. Name the coal-producing states in the United 
States. (See Figs. 116, 117, and 118.) 

In 1916 the United States produced over 300 million barrels 
of petroleum, more than two-thirds of which came from Okla- 
homa and California, the remainder coming from seventeen 
other states. The product of the United States was about two- 
thirds of the world's output, Russia and Mexico being the next 
largest producers (Fig. 119). 



THE LAND 



195 




Fig. 117. — Loading coal on railway cars at a bituminous coal mine in 
western Pennsylvania. (Photo by U. S. Geological Survey.) 




Fig. 118. — Map, showing distribution of coal fields in the United States. 
Shaded areas lignite, black areas bituminous coal, small black area in north- 
eastern Pennsylvania anthracite. 



196 



ELEMENTS OF PHYSICAL GEOGRAPHY 



The production of both coal and petroleum has increased at 
an enormous rate. In 1821, less than a century ago, the output 
of coal in the United States was only 1322 tons. The first 
petroleum marketed in the United States was in 1859, but 



1 1 






\ 1 


■S3 111 

H i 


M 


i$ H>S 


• "*'. 




%l IJH9 


' 


a 11 Jffi 






iMr fflEnt H iffl^Q 


r , KKBj 








*'■"' irlJBIl^iBr %tM3 






■ ?$SIsI5 



Fig. 119. 



•View of oil derricks at the Beaumont oil field, Tex. 
by U. S. Geological Survey.) 



(Photo 



little more than a half century ago, when 2000 barrels were 
produced in Pennsylvania. The increase in the output of both 
of these valuable fuels cannot continue many years. A maxi- 
mum will soon be reached. If the production decreases at 
the same rate as the increase, both these valuable fuels will 
soon be unobtainable. What do you think will take their 
place? 

Ferruginous rocks include the great beds of iron ore. 
Saline rocks include the beds of rock salt. 

Alkaline rocks include the borax and soda deposits occurring in 
arid districts. 



THE LAND 



197 



Igneous Rocks 

199. Igneous Rocks. — Igneous rocks, those which have 
cooled from a molten condition, are divided into two classes : 
(1) plutonic or granitoid, having a coarsely crystalline texture ; 
and (2) volcanic, having a glassy, stony, or porphyritic texture. 




Fig. 120. — View in a granite quarry at Bethel, Vt. (Photo by C. H. 
Richardson.) 

The granitoid rocks include those that cool slowly under 
pressure, hence they are coarsely crystalline and occur only 
in large masses that were formed deep below the surface and 
are now exposed because of the erosion of the overlying rock. 
They are composed of masses of interlocking crystals of dif- 
ferent kinds of minerals. The more common granitoid rocks are : 

(1) Granite, which consists of quartz, orthoclase feldspar, 
and generally one, two, or all three of the minerals mica, horn- 
blende, and augite. The micas are more common than the 
other two in granite (Fig. 120). 



198 ELEMENTS OF PHYSICAL GEOGRAPHY 

(2) Syenite, composed of orthoclase and hornblende, augite, 
or mica. It differs from granite in the absence of quartz. 

(3) Diorite, composed of plagioclase feldspar and hornblende, 
which thus differs from syenite in the presence of plagioclase 
in place of orthoclase. 

(4) Gabbro, composed of plagioclase, augite, and commonly 
magnetite and olivine, differs from diorite in having augite 
in place of hornblende. It is darker colored than diorite, which 
in turn is darker than granite and syenite. Diabase is more 
finely crystalline than gabbro. Basalt, which is still finer 
grained, belongs to the volcanic or intrusive class. The. last 
two form most of the trap rock which is used so extensively 
for making good roads. One of the best-known exposures is 
in the Palisades on the Hudson. 

The principal volcanic rocks are : (1) obsidian, volcanic 
glass; (2) pumice, rock froth, the very porous obsidian from 
the surface of a volcanic outflow ; (3) amygdaloid, the vesic- 
ular or coarsely porous form with the vesicles (holes formed 
by the escaping gas) filled with other minerals deposited from 
solution in the groundwater; (4) trachyte, with the same 
mineral content as syenite ; (5) andesite, with the same mineral 
content as diorite ; and (6) basalt, with the same mineral content 
as gabbro (trachyte, andesite, and basalt are the three principal 
stony varieties) ; (7) porphyry, which consists of a fine matrix 
with embedded crystals ; (8) volcanic tufa or tuff, composed 
of fragments of volcanic dust or cinders partially cemented or 
hardened. 

Pumice is used for grinding and polishing; numbers 4, 5, 
6, 7, and 8 are used for building stone, and some varieties of 
7 form a valuable ornamental stone. 

Metamorphic Rocks 

200. Metamorphic Rocks. — Metamorphic rocks are formed from 
either sedimentary or igneous rocks by a process known as meta- 



THE LAND 



199 



morphism, the chief agents of which appear to be water, heat, and 
pressure. Marble is metamorphic limestone and is more crystalline 
and generally harder and brighter colored than the original limestone. 
Slate is metamorphic clay or shale rendered much harder and stronger 
and finely crystalline. Anthracite is thought to be a metamorphic 
form of bituminous coal produced by pressure and heat. Quartzite is 




Fig. 121. — Metamorphic rock. A gneiss boulder near Arapahoe Peak, 
Colo. (Photo by the author.) 



a metamorphic sandstone with siliceous cement. Other metamorphic 
rocks are gneiss, serpentine, and schists of many kinds (Fig. 121). 

Selected specimens of the different rocks should be carefully studied 
and compared, and all the rocks found in the field trips should be 
named and classified. In many places in the northern United States 
specimens of nearly all the rocks described above may be obtained 
from deposits left by the glacier. 

201. Rocks and Minerals Useful to Man. — - A great many 
of the minerals and rocks are utilized by man directly or in- 



200 



ELEMENTS OF PHYSICAL GEOGRAPHY 



directly in his varied industries. Some, like coal and iron ore 
form the foundation of nearly all the manufacturing industries. 
From the rocks come the fuels, coal, oil, gas ; the ores of all 
the metals ; the building stones and other building materials, 




Fig. 122. 



Culm pile, waste from an anthracite coal mine at Scranton, Penna. 
(Photo by U. S. Geological Survey.) 



such as clay, sand, lime, and cement ; diamonds, other gems, 
jewels, ornamental stones of all kinds ; such useful articles 
as salt, sulphur, borax, nitre, phosphate, and many others. 

The science of Physical Geography is not directly concerned 
with the occurrence of these useful minerals, but man's ex- 
ploitation of these products becomes a geographic factor. 

In the region around Bedford, Indiana, hills have been re- 
moved by the limestone quarrymen in some places, and hills 
and basins formed in other places. Similar changes have been 
made in the sandstone quarry district in northern Ohio and 



THE LAND 201 

other quarry regions elsewhere. Whole ranges of hills have 
been removed in the iron ore districts about Lake Superior. 
Hills in great numbers have been formed through the coal 
regions of Pennsylvania and mining districts elsewhere, by the 
waste materials taken out in mining the coal (Fig. 122). Tun- 
nels and caverns of vast extent have been formed underground. 
Wells and springs have been destroyed. Surface streams have 
been polluted by mine waters. Streams have been diverted 
from their courses in the Sierra Nevada Mountains to wash 
the gold-bearing sands and gravels from the hills, to the de- 
struction of vegetation and the building up of flood plains in the 
valleys. In scores of ways in thousands of places the surface 
of the earth or its physical geography has been changed and 
modified by man's exploitation of the useful minerals and 
rocks. 

QUESTIONS 

1. Make lists of the common elements, the common minerals, and 
the common rocks. 

2. How is calcite distinguished from quartz, gypsum from feldspar, 
pyrite from gold, muscovite from biotite, halite from fluorite? 

3. Which of the minerals do you think is the most useful? Which 
ones have you seen mined or quarried ? 

4. Why do you suppose iron ore is imported into the United 
States from Cuba and Sweden when there is so much ore in this country ? 

5. Make a list of the localities from which you know copper is 
obtained. 

6. Why is copper used in larger quantities in war times than in 
times of peace? 

7. Make a list of articles made from aluminum. 

8. Iron, steel, and copper now (1919) cost much more than they 
did 20 years ago, while aluminum costs less. Why? 

9. What minerals are used in making soda water? 

10. Which ones are used in jewelry ? 

11. What mineral is used in our food ? 

12. Which ones are used in making powder? 

13. Which minerals are used by the farmers? 



202 ELEMENTS OF PHYSICAL GEOGRAPHY 

14. Make a list of the rocks that you have observed or can observe 
in the stone buildings of your town. Which one is used in largest 
quantities ? 

15. What rock quarries have you seen? Explain how the rock 
was quarried. For what was it used ? 

16. How can you tell a sedimentary rock from an igneous rock ? 

17. What kind of rocks do you think would occur in long, nearly 
straight ridges? 

18. What kind of rocks form high conical peaks? 

19. In what kinds of rocks do most caves occur ? Why ? 



CHAPTER VI 
MANTLE ROCK AND SOIL 

When the farmer leaves his plow in the field for a few days 
or weeks instead of putting it in the barn it becomes covered 
with rust. When rocks are left out in the air the same thing 
happens to them, they become covered with rust. This rock 
rust we call soil and in it grow the plants which furnish food 
for man and all other animals. 

The rusting of the rocks is a little more complicated than the 
rusting of the plow, and the resultant rust or soil is more com- 
plex than plow rust, because the rocks, as we have learned, are 
composed of a number of elements, while the plow is composed 
mainly of a single one, iron. Otherwise the process is much 
the same, the oxygen, the carbonic acid gas, and other sub- 
stances in the air combine chemically with the iron of the plow 
or the iron and other elements in the rocks, to form the rust 
or soil. 

In both eases the presence of water greatly hastens the rusting, in 
fact may even be the cause. If the iron or the rocks could be kept 
perfectly dry it is doubtful if they would ever rust. 

In both cases the presence of microscopic forms of life called bacteria 
hastens the rusting process. It is thought by many that the bacteria 
are essential and rusting would not take place without them. You 
have been ^warned of the danger from a scratch by a rusty nail or rusty 
knife. The danger is not in the iron rust itself, but in the bacteria 
contained in it. 

202. Weathering or Disintegration of Rocks. — The crum- 
bling of the hard rocks into waste or soil is called weathering and 

203 




Fig. 123. — Rock weathering from changes of temperature, etc., in which 
the blocks loosened on the cliff fall by gravity, breaking into smaller fragments 
in the talus at the base of the cliff. (Photo by B. W. Clark.) 

204 



MANTLE ROCK AND SOIL 205 

involves a number of different agencies. If the rocks did not 
weather or disintegrate, this world, devoid of life, would be 
a bleak and dreary world indeed. Fortunately, as soon as the 
rocks are exposed to the air, the disintegration to soil begins, and 
while it goes on slowly it goes on continuously all over the land 
areas (Fig. 123). 

203. Weathering Agents. — Other weathering agents acting 
with the air, water, and bacteria are changes of temperature, 
frost, wind, glaciers, streams, waves, gravity, plants, animals, 
and the chemical action of substances in the water and air. 
The disintegration is accomplished in part mechanically, in 
part chemically. The action of some of the agents is all me- 
chanical; with some it is purely chemical; with others it is 
both mechanical and chemical. 

The direct rays of the sun during the middle of the day heat 
the surface of the rock, causing it to expand. The surface is 
heated more than the interior, hence it expands more. This 
surface expansion is at times sufficient to cause fragments or 
layers to split off from the mass (Fig. 123). When the heated 
surface is cooled rapidly the contraction is sufficient to produce 
fracturing or breaking. When a camp fire is made on or against 
a rock mass, frequently fragments fly off with some violence 
from the heated surface, or if water is thrown on these 
heated rocks fracturing takes place. Disintegration in this 
way is most active in deserts and mountains, because there 
are more rock surfaces exposed and the extremes of heating 
and cooling are greater than elsewhere. The splitting off in 
sheets or flakes is called exfoliation (Fig. 124). Where the bed 
rock is cut into small angular blocks by numerous joint planes, 
disintegration in this way is called concentric weathering, and 
is exfoliation on a small scale (Fig. 125). 

When water is present in the rocks and the temperature 
falls below 32° F., frost or ice is formed. The expansion of 
the ice acts as a wedge to break the rock. A small quantity 



206 



ELEMENTS OF PHYSICAL GEOGRAPHY 




Fig. 124. — Weathering by exfoliation. Expansion and contraction of the 
surface from heating and cooling cause layers to split off parallel with the 
surface. (Photo by U. S. Geological Survey.) 



MANTLE ROCK AND SOIL 



207 



of moisture in small cavities near the surface of the rock wedges 
off small fragments; larger quantities freezing in cracks or 
larger cavities break off large masses. This agency is most 
active in cold temperate regions in the early winter and early 




Fig. 125. — Concentric weathering. Angular blocks of the bed rock dis- 
integrate more rapidly at corners and edges, changing the angular block to a 
rounded one ; further weathering causes the splitting off of concentric surface 
layers as in exfoliation. Compare Figs. 124 and 125. (Photo by Maryland 
Geological Survey.) 

spring, when there is thawing through the day and freezing 
at night. 

Wind blowing over a dry surface carries more or less sand 
and dust which wear fragments from rock surfaces against 
which it is blown. This is most prominent in deserts and 
semi-arid regions, where there is much sand and strong wind 
(Figs. 126 and 127). 

Glaciers are streams or sheets of ice moving over the surface 
of the land. The boulders and rock fragments frozen in the 



208 



ELEMENTS OF PHYSICAL GEOGRAPHY 



bottom of the glacier are pushed and rubbed against the bed 
rock with tremendous force, which wears the rock to fragments. 
Glaciers are most active in high mountains and high latitudes. 
(See Chapter IX.) 
Streams of water frequently have sufficient velocity to carry 




Fig. 126. — Differential weathering. Rocks sculptured by wind erosion. 
(Photo by W. B. Heroy.) 



along mud, sand, gravel, and boulders, which, striking against 
the bed rocks in the channel, wear away both the bed rocks 
and the fragments. This is an active agency in hills and 
mountains, where swift streams flow over rocks. Similar 
grinding up of the rocks is produced by waves on the beach 
(Fig. 128). 



MANTLE ROCK AND SOIL 



209 



Gravity becomes an agent of disintegration on mountain 
slopes and hillsides, where fragments large and small are 
loosened and roll or fall down the slopes. Not only the mass 
which falls is liable to break into fragments, but the rock upon 




Fig. 127. — Differential weathering, 
rain erosion, Bad Lands, S. Dak. 



Rocks weathered chiefly by wind and 
(Photo by U. S. Geological Survey.) 



which it falls is apt to be crushed. This is most noticeable 
at the foot of steep cliffs. The mass of angular fragments 
at the base of the cliff is called talus. (See Figs. 123 and 129.) 

The roots of small plants extending into fine cracks on the sur- 
face of rocks wedge off fragments and grains of rocks. The roots 
and trunks of trees growing in large cracks split off large frag- 
ments. This takes place on all rock surfaces where vegetation 
is growing (Fig. 130). 

All of the agents described above act mechanically in breaking 
the rock into fragments and the fragments into smaller ones. 
Plants, however, act chemically as well, when the acids from the 



210 



ELEMENTS OF PHYSICAL GEOGRAPHY 




Fig. 128. — Rock disintegration by stream action, Stanislaus River, Calif. 
(Photo by U. S. Geological Survey.) 



MANTLE ROCK AND SOIL 



211 



roots of the growing plants and from the decaying vegetation 
a ttack the mineral compounds and dissolve one or more elements 
of a mineral, causing the remainder to crumble to fragments. 




Fig. 129. — Disintegration by gravity and other agents. See also Fig. 123. 
(Photo by B. W. Clark.) 




Fig. 130. — Growing trees aid in rock disintegration by trunk and roots splitting 
large boulders. View near Owasso, Okla. (Photo by B. C. Loveland.) 



212 ELEMENTS OF PHYSICAL GEOGRAPHY 

Water is the most universal agent in the chemical disinte- 
gration of rocks, not alone in dissolving portions of the minerals, 
but in serving as the carrier or transporting agent of all the other 
elements and compounds that produce weathering of rocks. 




Fig. 131. — Differential weathering of massive white sandstone on Freezeout 
Mountain, Wyo. (Photo by the author.) 



204. Oxygen and Carbonic Acid. — Oxygen and carbonic 
acid, two of the most abundant agents of chemical weathering, 
would have but little effect on the rocks if they were not brought 
into contact with them through the agency of water; but 
in the presence of water they become the most important 
weathering agents. Oxygen attacks iron pyrite, widely 
scattered through the rocks. It combines with the sulphur, 
finally producing sulphuric acid, which breaks up other mineral 



MANTLE ROCK AND SOIL 213 

compounds. Oxygen also combines with the iron in horn- 
blende and other minerals, causing them to crumble. 

Carbonic acid in the water dissolves limestone and other 
carbonate rocks, carrying the carbonates away in solution 
and leaving the insoluble parts of the rocks as residual soil. 
Carbonic acid also attacks the potash, soda, and lime in the 
feldspars and some other minerals, causing them to crumble 
to clay and sand. 

The chemical combinations started by the oxygen, carbonic acid, 
the organic acids from plants and animals, the nitric and other acids, 
continue through the rock mass, breaking up old mineral compounds 
and forming new ones, much of the chemical activity resulting finally 
in reducing the hard minerals to fine clay, sand, and silt particles, which 
form the soil. 

Since the chemical action is most vigorous in the presence of water 
and is also aided and intensified by the bacteria, which also require 
water, it is most effective in warm, moist regions, and least active 
in deserts and extremely cold regions. In tropical and subtropical 
regions the rocks are disintegrated mainly by chemical agents, often 
to depths of several hundred feet. 

205. Animals as Agents of Disintegration. — The animals 
that are most important in weathering or disintegrating rocks, 
are those that burrow in the ground, such as certain bacteria, 
worms, ants, beetles, crayfish, squirrels, gophers, prairie dogs, 
woodchucks, badgers, and foxes. They aid in weathering 
directly by breaking the fragments into smaller ones in forming 
their burrows, indirectly in making openings through which 
other agents, such as water and air, gain access to fresh rock 
surfaces, and further by acids formed from their remains and 
refuse. 

Ants extend their excavations sometimes many feet below 
the surface by carrying small rock fragments to the surface, 
building up mounds several feet in height. They secrete a 
stringent acid which acts chemically on the rocks with which 
it comes in contact. 



214 ELEMENTS OF PHYSICAL GEOGRAPHY 

Earthworms are probably the most important of all animals, 
unless it is man, in disintegrating rock material, because of their 
great numbers, wide distribution, and vigorous action. The 
worms pass the earth through their bodies, where it is mechan- 
ically ground finer and also disintegrated by the chemical 
action of the organic matter. They burrow to great depth in 
dry weather and carry vast quantities of rock material to the 
surface. Darwin estimates that in a moist climate like that 
of England, the earthworms bring to the surface from varying 
depths not less than ten tons of rock material per acre every 
year. The aggregate results produced by these lowly creatures 
during the centuries are surprisingly great. 1 

Larger animals, such as bison, elk, deer, cattle, and horses, 
are agents of mechanical disintegration of rocks in wearing off 
fragments by the impact of their hard hoofs as they travel 
over them. 

206. Other Disintegrating Agencies. — Rocks are disinte- 
grated or broken into fragments by volcanic explosions and by 
fracturing along faults or fractures in earthquake movements. 
These are not ordinarily classed as weathering agents, nor are 
they so widespread in their action as the weathering agencies 
described above. Locally, however, they break up and pulver- 
ize rocks in large quantities. 

During the volcanic eruption of Krakatoa in the East Indies 
in 1883, two-thirds of the island, composing millions of tons 
of rocks, was blown to fragments, much of it exceedingly 
fine dust. Some of the dust was distributed by the atmosphere 
over a large part of the earth. During several eruptions of 
Mt. Vesuvius (Fig. 132) and the great eruption of Mt. Pelee 
vast quantities of dust and fragmental rock were blown into 
the air, which, falling over the surrounding regions, formed 
deposits of great thickness over many square miles of surface. 

1 Darwin's classic little book on Earthworms is profitable reading for any one 
interested in the study of soil. 



MANTLE ROCK AND SOIL 215 

Most volcanic dusts form very productive soil. The great 
wheat region of eastern Washington has volcanic dust soil 
(Fig. 133). 

207. Mantle Rock. — All of the loose fragmental material, 
produced by the combined action of the above mentioned and 




Fig. 132. — Rocks disintegrated by volcanic action, summit of Mt. Vesuvius. 

all other weathering and disintegrating agencies, which rests 
upon the solid bed rock like a mantle, is called mantle rock. 
This mantle rock covers the bed rock almost everywhere except 
in rock quarries, rock cliffs, and a few other places. 

In some places the line of separation between the mantle 
rock and the bed rock is sharply defined, in other places the 
change from one to the other is so gradual that there is no sharp 
line of separation between them. In the first case the frag- 
mental material has been moved by ice, water, wind, gravity, 



216 



ELEMENTS OF PHYSICAL GEOGRAPHY 



or man, and deposited on bed rock. In the other the weather- 
ing agents are working down from the surface. (See Figs. 134 
and 136.) 

208. Thickness of the Mantle Rock. — The mantle rock varies 
in thickness from a mere film up to several hundreds of feet. 



. » »,.«. J » T <i rt1 ■ Mi l 




Fig. 133. — Wheat field on productive volcanic soil on the Columbia Plateau, 
eastern Washington. (Photo from Spokane Chamber of Commerce.) 



In the city of Washington the granite rock is partially disin- 
tegrated to a depth of 80 feet or more. In Brazil the mantle 
rock is in places 400 feet deep. Such thicknesses do not occur 
in cold regions except where the material has accumulated by 
some transporting agent. In filled valleys, in talus slopes, in 
alluvial fans, in deposits left by a glacier, or in accumulations 
formed by man, it may be hundreds of feet deep. But the 



MANTLE ROCK AND SOIL 



217 



disintegrating agencies do not penetrate as deep in cold regions 
as they do in warm. 

209. Transportation of Mantle Rock. — Mention has been 
made of the shifting or transportation of mantle rock ; in fact, 
as soon as the weathering agencies begin the disintegration of 



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Fig. 134. 



Gradation of soil into partially disintegrated granite on Flagstaff 
Mountain, Boulder, Colo. (Photo by the author.) 



bed rock, the transporting agencies begin to carry it away. 
Hence the thickness of the mantle rock at any one place is 
simply the accumulation due to the excess of weathering over 
transportation, or the amount deposited at any place by 
the carrying agents. 

Since the disintegration of rocks by weathering, and the re- 
moval of the fine material by the transporting agents, have 
been going on continuously through all the ages past, it follows 
that on the older land areas enormous quantities of the bed 



218 ELEMENTS OF PHYSICAL GEOGRAPHY 

rock have been disintegrated and removed. It is estimated 
that on the areas where Philadelphia and New York City are 
located, many thousands of feet, in fact several miles in 




Fig. 135. — Section across Nittany and Bald Eagle Valleys, Center Co., 
Penna., indicating by dotted lines part of the enormous thickness of rocks 
that have been removed by erosion. 

thickness, of rock have been removed. (Study Fig. 135 and 
see how such estimates are made.) 

The final resting place of the transported mantle rock is the 
sea bottom, hence the mantle rock now on the continents is 
the disintegrated product that has not yet been removed, and 
is only a small fraction of the large amount that has been 
carried to the sea in ages past. (The action of the transporting 
agents is discussed in Chapters VIII and IX.) 

210. Soil. — Sometimes all of the mantle rock is called soil, 
but soil to the farmer is only the surface portion of the mantle 
rock, in which he plants his seeds. The part underlying this 
he calls subsoil or under the soil. On the flood plains along 
the river bottoms, on most of the prairie lands, and on the muck 
or black land areas, the soil is frequently many feet in thick- 
ness, and if there is any subsoil it is never seen. But in most 
of the hillsides and the uplands outside of the glaciated regions, 
the soil of the farmer is only a few inches deep and the plow 
frequently turns up portions of the subsoil. When the soil 
is plowed to the same depth for several years a hard crust 
known as the " plow sole " is formed on top of the subsoil. 
The roots cannot penetrate this and poor crops result. This 



MANTLE ROCK AND SOIL 219 

can be prevented in part by varying the depth of the plowing 
from year to year. 

In some places a hard pan is formed under the soil by the 
carbonate of lime or iron which is dissolved in the surface soil 
and precipitated in the subsoil. Such areas are very poor 
farm land. Trees planted on such areas grow for a few years 
and then die because the roots cannot penetrate the hard pan. 
This is remedied in some places by using dynamite to blast 
a hole in which the tree is planted. The dynamite breaks 
the hard pan and the roots can then penetrate to greater depths. 

Humus in Soil. — Soils have variable quantities of 
humus formed from decaying vegetation and bacteria, both 
of which add to the productiveness of the soil and are thought 
to be necessary. The mixture of the organic matter with the 
mineral matter of the soils is accomplished in several ways. 
Earthworms, ants, and other burrowing animals carry vegetable 
material down into the soil and fresh rock material to the 
surface, thus mixing and fertilizing the soil. The farmer aids 
in this process by the use of the plow and the cultivator. The 
roots of the plants form another aid. 

211. Kinds of Soil. — The body or bulk of nearly all soils is 
made up of clay, silt, and sand, sometimes mixed with gravel or 
rock fragments. If the clay is greatly in excess, the soil is called 
clay soil and is apt to be cold, heavy, and wet, in contrast with 
one composed mostly of sand, or sandy soil, said to be warm, 
light, and dry. Better than either of these for most crops is 
the loamy soil, which consists of a somewhat equal mixture of 
clay and sand, or is composed mostly of silt. Where the gravel 
is abundant it forms gravelly or stony soil. Muck soil is com- 
posed of the remains of plants accumulated in swamps or bogs. 
It is the soil of the black lands of northern United States and is 
generally very productive where the excess water has been 
drained off. Much of it is used for growing celery, onions, 
and. other vegetable garden crops. 



220 



ELEMENTS OF PHYSICAL GEOGRAPHY 



212. Residual Soil. — Residual soil occurs in the place 
occupied by the bed rock from which it is disintegrated. It 
forms the greater part of the upland soils in all but glaciated 




Fig. 136. 



Residual soil on limestone, weathered by solution, soil partly re- 
moved in the foreground. See also Fig. 134. 



regions, and depends for its character and qualities on the 
underlying rock from which it is derived. The different kinds 
of rocks produce different kinds of soils (Fig. 136). 

213. Transported Soils. — Often soil is not residual, but has 
been moved from the place where disintegration took place. 
The transporting agents are water, ice, wind, and gravity. 

214. (a) Alluvial Soils. — Alluvial soils are those formed 
on river flood plains and deltas. They are commonly known 
as " bottom lands," that is, formed on the bottom of the valley. 
They consist of the material washed from the hillsides and 
mountain sides by the rains, and deposited on the flats along 
the stream. They rank with the richest and best of all soils 



MANTLE ROCK AND SOIL 



221 



(Fig. 137). In flood season they are subject to overflows, which 
sometimes prove destructive, but there is some compensation 
in a layer of new rich soil left by the subsiding flood. The 
soil of alluvial fans differs somewhat from the common flood 
plain deposits. (See Chapter VIII.) 




Fig. 137. 



■ Threshing scene on the alluvial soil of the Sacramento Valley, 
Calif. (Photo by U. S. Department of Agriculture.) 



215. (6) Glacial Soils. — Glacial soils are those left by the 
disappearance of a former glacier. All northeastern United 
States and the central part north of the Ohio and Missouri 
Rivers was formerly covered by a continental glacier or sheet of 
ice, which left on the surface the mantle rock that had been 
moved by the ice. (See Chapter IX.) While the glacial soils 
are not all good, on the whole the productiveness has been 
improved by glacial action, because they consist of mixed soil 
from many different kinds of rocks, and in part of freshly 
ground-up bed rock from which the food elements, such as 



222 ELEMENTS OF PHYSICAL GEOGRAPHY 

potash, phosphate, etc., have not been leached out by percolat- 
ing groundwater. However, there are many varieties of glacial 
soil. Glacial soils cover large areas in the valleys and around 
the borders of the Rocky Mountains and the Sierra Nevada 
and Cascade Mountains of western United States (Fig. 138). 




Fig. 138. — Glacial soil at Syracuse, N. Y. (Photo by the author.) 

216. (c) Lacustrine Soils. — Lacustrine soils are those formed 
on lake bottoms. While they vary considerably in kind, most 
of them may be grouped under one of three types : (1) the 
fine mud and silt washed from the surrounding area and spread 
over the lake bottom, which forms the surface soil when the 
lake is drained or filled, or the water evaporated. Such are 
the rich wheat lands of the Red River Valley of North Dakota 
and Manitoba'; (2) the black muck soil formed of vegetable 
matter that sometimes fills shallow lakes ; (3) shell marl formed 
largely of the remains of small shells and lime-secreting plants. 



MANTLE ROCK AND SOIL 



223 



217. (d) Colluvial Soils. — ColLuvial soils are those formed 
in many valleys and basins in the mountains of the west and 
southwest by the combined action of gravity and rain wash, 




Fig. 139. — Gully eroded in loess soil at Helena, Ark. Loess stands in vertical 
cliffs better than any other variety of soil. (Photo by U. S. Geological Survey.) 

which have carried the fine material from the mountain slopes 
over the lowlands at the base. 

218. (e) Loess Soils. — Loess soils cover extensive areas 
in the Mississippi basin, especially the western part of it. 



224 ELEMENTS OF PHYSICAL GEOGRAPHY 

They include some of the best farms of the Mississippi basin. 
Loess soils occur in China, Germany, and elsewhere. They are 
dust deposits, thought to be formed by the wind (Fig. 139). 

219. (/) Alkali Soils. — These occur only in dry regions. 
They are common in the arid and semi-arid regions of the west 
and southwest, where evaporation is in excess of precipitation. 




Fig. 140. — Alkali soil at Alkali Buttes, Weston Co., Wyo. See also 
Figs. 252 and 287. (Photo by U. S. Geological Survey.) 

Some of the alkali is the accumulation washed from surround- 
ing areas, some of it is brought to the surface by capillarity, 
the water evaporating and leaving the alkali on the surface. 
An excess of alkali in the soil makes it unproductive (Fig. 140) . 

There are many other soil types, such as " gumbo soils," 
" crayfish lands," " salt lands," " hard pan," " volcanic soils " 
(formed by the dust thrown out in volcanic eruptions), etc. 

220. Productive Soils. — Some plants derive all their 
nourishment from the air and water, but most of them, in- 
cluding practically all those cultivated for food, derive part 
of their food from the soil. It is well known by the farmer 



MANTLE ROCK AND SOIL 225 

that some of his soils produce larger crops than others. Pro- 
longed investigation has shown that the productiveness of 
different soils depends upon the physical condition, the methods 
of tilling, and the constituents in the soil. The mineral con- 
stituents of the soil used as food by the plants are phos- 
phates, potash, nitrogen in the form of nitrates, and, in smaller 
quantities, lime, iron, etc. Humus formed by the decaying 
vegetation and bacteria are other important if not necessary 
constituents of a productive soil. 

It happens that practically all these constituents are present 
in most virgin soils. But when the soils are tilled, each crop 
takes up a certain amount of these food elements. Where 
the crops are taken off year after year and nothing returned 
to the soil, it is clear that in time the soil will become poorer 
and poorer in food supplies, until the crops become so small 
that it no longer pays to farm it. 

221. Soil Conservation. — Some crops take more of one 
substance and others more of another, hence the importance 
of a proper rotation of crops. The intelligent farmer discovers 
which plant foods are needed in his soil and adds them from 
time to time, thus keeping up or even improving the fertility 
of the soil. Fields which have received proper attention are 
as productive now as they were centuries ago ; while others, 
through lack of care, become unproductive in a few years. 
The application of science and scientific methods enables the 
farmers today to feed more than a hundred million people 
in this country and millions in other countries, which could 
not possibly be done by the primitive farming methods of 
the Indians. 

Many people are just beginning to realize the possibilities 
in the soil and the necessity for its scientific study and culti- 
vation if we are to supply the increasing demand for food with 
increasing population. Each year finds a smaller percentage 
of the people engaged in farming and a larger percentage in 



226 ELEMENTS OF PHYSICAL GEOGRAPHY 

manufacturing, commerce, and other occupations. By fur- 
nishing improved machinery and improved methods of trans- 
portation the non-farmers help the farmer to market his crop. 
But the farmer must apply scientific methods in order to have 
the crops to market. 

QUESTIONS 

1. What happens to iron implements left on the surface of the 
earth ? 

2. Does an iron bridge or locomotive rust as rapidly as a plow left 
in the field? Why? 

3. What causes rocks to rust? Why do some rust faster than 
others ? 

4. What kind of weathering agents are most active in a dry 
climate ? In a moist climate ? In a cold climate ? 

5. Why do rocks weather faster on the south side of a hill than on 
the north side ? Would this be true in Argentina ? 

6. State all the different ways in which plants and animals aid 
in changing rocks to soil. Underscore all those which you have 
observed. 

7. What is the distinction between mantle rock and soil? Be- 
tween soil and subsoil? 

8. Why are soils generally deeper on a plain than on a steep 
hillside ? Why are they frequently absent from a very steep hillside ? 

9. Farm lands in many of the valleys of the Allegheny Moun- 
tains are worth from $50 to $200 an acre, while much of the land on 
the mountains is not worth $5 an acre. State three or more good rea- 
sons for the difference. 

10. Why are the black soils generally better than the gray soils ? 

11. Why are red soils generally better than yellow soils? 

12. What are the principal farm crops produced in your vicinity? 

13. What farm machinery have you seen in operation? 

14. Enumerate the different uses made of the gasoline engine 
in modern farming. 



CHAPTER VII 
GROUNDWATER 

222. Circulation of Water. — The atmosphere contains 
moisture, some of it visible in the form of clouds, bujb most of 
it invisible as water vapor. (Chapter II.) The quantity of 
moisture in the air varies from time to time and from place to 
place. Warm air has a greater capacity for moisture than cold 
air. If the temperature of air that is saturated with moisture 
is lowered, some of the water is squeezed out and falls to the 
earth in the form of rain or snow. What becomes of the rain 
and snow? 

Some of the precipitation is evaporated and passes again into 
the atmosphere, some of it sinks into the earth, some of it runs 
off the surface in streams which finally carry it back to the 
ocean. Hence, there is a circulation of water from the ocean 
through the air to the lands and back again to the ocean. 

The circulatory water not only aids the other weathering agents 
in disintegrating the hard rocks, but it carries away the weathered 
material with it on its journey back to the sea. It is this circulation 
and the work done on the journey that makes life possible, on both 
the land and the sea. All forms of life are made up of elements derived 
in part from water, in part from the air, and in part from the rocks, 
and the circulation of the water brings all these to the living forms. 

223. Groundwater. — The part of rain and snow that sinks 
into the earth is called groundwater or underground water. 
The proportion of rainfall that becomes groundwater varies 
from place to place and from time to time. (1) There is a 
larger percentage of groundwater where the rain falls on sand 

227 



228 ELEMENTS OF PHYSICAL GEOGRAPHY 

or broken rock than if it falls on bed rock or baked clay sur- 
face. (2) More sinks into the earth on a flat surface than on 
a steep slope. (3) In a slow drizzling rain a larger percentage 
sinks into the earth than in a dashing rain, where much of it 
flows off. (4) A frozen surface causes greater run-off and less 
groundwater. (5) In arid and semiarid regions there is more 
evaporation and greater run-off on the slopes, hence less ground- 
water than in a humid region. 

224. Movements of Groundwater. — The groundwater 
moves down into the earth by force of gravity, capillarity, and 
pressure of the overlying water. It moves faster through large 
openings than small ones, faster through the more porous rocks 
only when the pores are larger. Clay has many more pores 
than sand or sandstones, but the pores are much smaller, hence 
groundwater moves much faster through sand or gravel than 
through clay. Layers of rock through which groundwater 
moves most rapidly, such as coarse sandstone and conglomerate, 
are called aquifers. The size of the aquifers and their relation 
to the surface and to the water table are often determining factors 
of the value of artesian wells, common wells, and springs. 

The groundwater passes through some rocks more readily than 
others, but none of the rocks near the surface are so dense as entirely 
to stop the downward movement. However, as it penetrates deeper 
into the earth the pressure of the overlying rocks begins to close the 
pores, until at a depth of ten or eleven miles it is thought they are 
entirely closed against the movement of water. This is the lower 
limit of the groundwater. The upper limit is the water table. 

225. The Water Table. — The water table is the upper 
limit of the zone of saturation. It is at the surface of the 
ocean, of most lakes, swamps, and permanent streams. In the 
land areas between these water bodies the water table occurs 
at depths varying from a few feet to hundreds of feet. It rises 
in the land areas, but generally does not rise as rapidly as the 
slope of the land. Hence it is higher above sea level, but deeper 



GROUNDWATER 



229 



below the surface, in the hills and plateaus than in the valleys 
and plains (Fig. 141). In general it is deeper in arid regions 
than in humid ones, deeper in dry seasons than in wet seasons. 




Fig. 141. — Showing position of water table. 



226. Fluctuations of the Water Table. — The position to 
which the water table sinks in dry seasons is called the per- 
manent water table. During the rainy season the groundwater 
accumulates on top of the permanent water table and raises it 
to a higher position, called the temporary water table. The 
level of the water in ordinary wells denotes the position of the 
water table. If a well becomes full in wet seasons it means the 
temporary water table has risen to the surface. If a well goes 
dry it means that the water table has sunk below the bottom 
of the well. 

227. Lateral Movement. — The water at and below the 
water table in the hills is continually moving, laterally down the 
slopes wherever the water table has any slope ; that is, water 
in the ground, like water on the surface, seeks a common level, 
and there is a movement as long as there are any inequalities 
in the surface of the water table. It is this lateral movement of 
the groundwater that supplies the water in the wells and springs 
and in streams. If precipitation should cease entirely, in time 
the surface of the water table would sink down and become 
continuous under the lands at sea level. The lateral movement 
of the water is so slow that long before the water table is lowered 
very much, the supply from rains or melting snows raises it 



230 ELEMENTS OF PHYSICAL GEOGRAPHY 

again, and the fluctuation of the water table at any place 
differs but little more than the rainfall from season to season 
or from year to year. 

228. Work of the Groundwater. — In the percolation of 
the groundwater through the pores and cavities of the rocks 
it is an active agent, in some places destructive and in some 
places constructive. That is, in some places it tends to break 
down and disrupt the rock mass through which it is percolating, 
in other places it builds up masses of rock material. In the 
preceding chapter it was explained that some of the mineral 
compounds forming the rocks are soluble in water, and most of 
the minerals are wholly or partly soluble in the acids and other 
materials dissolved in the groundwater. Hence, it becomes 
one of the most active agents of disintegration in changing the 
hard bed rock to loose mantle rock. We are now ready to con- 
sider more special phases of this work. 

229. Destructive Action of Groundwater. — The percolation 
of groundwater through the rocks acts as a destructive 
agent to the bed rocks, taking part of the mineral matter in 
solution and carrying it through the springs and streams to 
the ocean, and changing the part that remains to mantle 
rock. The destructive activity is in general greatest above 
the water table, and the constructive action greatest below the 
water table. 

230. Caves. — Carbon dioxide, derived partly from the air 
and partly from the soil, dissolves limestone when it is brought 
in contact with this rock by the percolating groundwater, which 
likewise acts as the agent to carry away the material after it 
is dissolved. In this way such caves as Mammoth Cave in 
Kentucky, Luray in Virginia, Wyandotte and Marengo in 
Indiana, Wind Cave in South Dakota, and Howe's Cave hi 
New York are formed. (See Figs. 142 and 143.) 

The above are some of the best -known caves in the United States, 
but there are hundreds of similar ones not so widely known. Nearly 



GROUNDWATER 



231 



every bed of limestone has numerous caverns large or small. In the 
upland areas of central Kentucky it is estimated that there are not 
less than 10,000 miles of limestone caverns. Limestone caves vary 
in length from a few feet to many miles, in depth below the surface 





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///->■ y ti i 










i i i i i i i * r 





Fig. 142. — Diagram showing caves and sink holes in limestone 
talus slope at the left. 



Cliff and 



from a few feet to several hundred feet. Mammoth Cave has been 
explored over 100 miles ; possibly as much more remains unexplored. 

Wind Cave, near the Black Hills, South Dakota, has been made a 
national park, and four other caves are now national monuments, 
namely, Lewis and Clark Cavern, Montana ; Shoshone Cavern, Wyo- 
ming ; Jewel Cave, South Dakota ; and Oregon Caves, Oregon. 

231. Life in Caves. — As might well be imagined, caves fre- 
quently form retreats or hiding places for different animals, the 
most common being the bats, which fly abroad in summer nights, 
but spend the days and the winter seasons in the caves, where 
they sometimes cluster in great masses, hanging from the roof 
of the cavern. Beetles, lizards, mice, wolves, bears, and foxes 
are some of the other animals that find a home in caves. Blind 
fish are sometimes found in them. 

Savage man in past ages found shelter there. Relics of his 
handiwork, his. implements, and his carving on the walls have 
been found in different caves, often associated with bones and 
pictures made by him of now extinct animals, and even with 
the bones of primeval man. 

One of the products of life in caves is nitre or saltpeter, which 
has been a source of supply for powder-making in time of need. 



232 ELEMENTS OF PHYSICAL GEOGRAPHY 




Fig. 143. — Map of portion of the explored galleries in Mammoth Cave, 
Ky. More than 100 miles of galleries have been traversed in the cave. The 
openings are at several different levels and vary in height from a few feet to 
more than 200 feet. Shaded portions contain water. Scale about lj miles to 
the inch. 



GROUNDWATER 



233 



The old vats in which saltpeter was made many years ago still 
remain in Mammoth Cave, Kentucky. Other caves furnished 
this much needed commodity during both the Revolution and 
the Civil War. 

232. Corrading Action of Cave Streams. — Besides the 
dissolving action of the groundwaters there is in places a cor- 




Fig. 144. 



■ Sink hole in limestone in eastern Wyoming. 
Geological Survey.) 



(Photo by U. S. 



rading or wearing action on the bottoms and sides of caves 
similar to the work of surface streams. In some places several 
caves occur one above the other. The upper ones are dry 
while the lowest one frequently has a stream in part of the 
cave. Most of the corrading work done in caves is not done 
by the permanent stream, but by the temporary streams that 
pour in through openings in the roof during the rainy seasons. 



234 



ELEMENTS OF PHYSICAL GEOGRAPHY 



Lost River in Indiana flows through limestone caverns for about 
ten miles of its course, but in the flood season, when there is more 
water than can find escape through the underground channel, the 
surplus flows in the surface channel until the flood subsides, when it 
disappears into the cave. Presumably there is considerable corrasion 
in such a cave. There are many such "lost rivers" in the limestone 
valleys of the Allegheny Mountains. They differ from the so-called 
"lost rivers" in arid and semiarid regions in which the stream water is 
partly evaporated and the remainder sinks through the sand and gravel. 

233. Sink Holes. — In nearly every limestone region where 
there are caves there are numerous basin-like or funnel-shaped 




Fig. 145. 



■ Karsten, roughened surface of limestone produced by solution along 
cracks and fissures. (Photo by the author.) 



depressions, called sink holes or swallow holes. The large open- 
ing serves to catch the rainfall and to lead it into the narrow 
opening at the bottom, corresponding to the stem of the funnel. 
Through the sink hole the surface water drains into larger 
caverns. (See Figs. 142 and 144.) 

A limestone surface much diversified by the action of the ground- 
water dissolving the rock along cracks and joint-planes, thus leaving 



GROUNDWATER 



235 




Fig. 146. — Trick Falls in Glacier Xational Park. In dry seasons there is no 
water on the upper falls. See Fig. 146a. (Photo by Winter Photo Co.) 



236 ELEMENTS OF PHYSICAL GEOGRAPHY 

many deep irregular fissures, is called by the Germans the Karsten. 
There is no English word for this phenomenon, although it occurs in 
many places in New York and elsewhere in the United States. (See 
Fig. 145.) 

234. Natural Bridges. — Natural bridges are formed some- 
times by the breaking down of part of the roof over one of 
these subterranean streams. The portion of the roof that re- 
mains, spanning the now open chasm, is called a natural bridge. 



Lake Two 




Fig. 146a. — Diagram at Trick Falls, on Two Medicine River. A, top of 
upper falls in wet season, no water in dry season. B, lower falls. C, opening in 
river channel into which all the water flows in dry seasons, part of it in wet 
seasons. The opening at C will increase in size until falls will be at C, and as 
the block of limestone E weathers away at A and C it will form a natural bridge 
across the stream. 

The famous Natural Bridge in Virginia was formed in this way. A 
similar natural bridge is now in process of formation at Trick Falls in 
Glacier National Park. (Study the photo and the diagram, Figs. 146 
and 146 a.) 

The longest natural bridges in the world, in Southern Utah, were 
formed on an entrenched meandering stream, which has undercut the 
sandstone in the necks of the meanders (Fig. 147). Some of these, 
Natural Bridges and Rainbow Bridge, have been set aside as national 
monuments. (See also Figs. 65 and 71.) 

235. Landslides. — Groundwater is frequently an important 
agent in producing landslides. On steep hillsides where some 
of the supporting material has been removed from the base 
by stream erosion or by excavations made by man, landslides 
are common. The slides are facilitated by the groundwater, 
which increases the weight of the overlying material and also 
acts as a lubricant in the saturated rock. 



GROUNDWATER 237 

In the Culebra Cut on the Panama Canal there have been 
many slides, and these will continue until the steep slopes pro- 
duced by the excavation have been reduced to the angle of 
rest for the saturated rock material composing them (Fig. 148) . 




Fig. 147. — Sandstone Natural Bridge. The largest natural bridge in the 
world. Formed by undercutting of the creek. (Photo of painting loaned 
by E. F. Holmes.) 

In the Allegheny Plateau the grading of the railway lines, con- 
structed along the bottom of the valleys, have necessitated excava- 
tions in many places, thus artificially steepening the slope. After 
prolonged wet seasons, when the mantle rock on these steepened slopes 
becomes saturated with groundwater, landslides are of frequent oc- 
currence. 

In mountainous regions landslides sometimes prove destructive 
to human life and produce quite marked changes in the topography. 
In 1806 a landslide in the Alps Mountains in Switzerland buried the 
village of Goldau, killing several hundred people. In another part 
of the Alps the material of a great landslide built up hills nearly 200 
feet high in the Rhone Valley. In 1893 a landslide estimated to con- 
tain about 800,000,000 tons of rock occurred in the Himalaya Moun- 



238 ELEMENTS OF PHYSICAL GEOGRAPHY 




GROUNDWATER 



239 



tains. The material of this slide built a dam nearly 1000 feet high 
across one of the tributaries of the Ganges River, forming a lake four 
miles long. 

The village of Frank, in the Province of Alberta, was partly de- 
stroyed by a great landslide which killed more than 60 people. About 




Fig. 149. 



Landslide on Turtle Mountain, Frank, Alta. The rock 
here was in hard limestone. (Photo by the author.) 



slide 



4,000,000 tons of rock fell from the end of Turtle Mountain into the 
valley at the base and buried nearly a mile of the Canadian Pacific 
Railway (Fig. 149). 

The slow, scarcely perceptible movement of the loose material 
on the slopes is called creep. Intermediate between the creep and 
sudden landslide is the mud flow that occasionally takes place on 
a clay slope when the clay becomes saturated with groundwater. 
(Fig. 150.) 

236. Constructive Action of Groundwater. — Some of the 
mineral material taken in solution by the groundwater is carried 
to the ocean, while part of it is deposited again, sometimes on 



240 ELEMENTS OF PHYSICAL GEOGRAPHY 

the surface where the groundwater emerges, and sometimes 
underneath the surface. In percolating through the rocks, 
the water and the carbonic acid gas in the water are under 
pressure and hence take up more carbonate of lime than they 




Fig. 150. — Creep in slate, near Columbia, Pa. In the upper half of the 
view the vertical layers are broken and creeping down the slope to the right. 
(Photo by U. S. Geological Survey.) 

can hold in solution under less pressure ; hence, when the 
water reaches a cavity or the surface, where the pressure is 
lowered, some of the acid gas escapes into the air, some of the 
water is evaporated, and part of the mineral matter is deposited. 
237. Veins. — When the mineral matter carried in solution 
is deposited in cracks or fissures in the rocks, it forms veins, in 
which are formed compounds or ores of different metals, such 
as gold, silver, lead, zinc, copper, etc. Mingled with the ores 
are variable quantities of other minerals, known as gangue or 



GROUNDWATER 



241 



vein-stuff, consisting of calcite, fluorite, barite, quartz, and other 
minerals, all of which are carried by the groundwaters into 
fissures and there deposited to form veins. Man is largely 
dependent upon these veins for the supply of metals needed 




Fig. 151. — Small calcite veins formed by deposition of carbonate of lime 
in cracks in limestone. (Photo by U. S. Geological Survey.) 



in the different industries, because in the original condition 
of the rocks the metals are so scattered and diffused that they 
cannot be profitably extracted until they are segregated as ores 
in the veins by the action of groundwater (Figs. 151 and 152). 
238. Cave Deposits. — The water that very slowly drips 
from the roof of a limestone cave is partly evaporated and at 
the same time permits the escape of part of the carbon dioxide, 
which causes part of the lime carbonate to be precipitated in 
the. form of an icicle-like deposit called a stalactite. A cor- 



242 ELEMENTS OF PHYSICAL GEOGRAPHY 

responding projection built up on the floor of the cave is called 
a stalagmite. How can you prove that these are carbonate of 
lime? Many of the stalactites have a small hole running 
lengthwise through the middle. How do you account for it? 




Fig. 152. — Gold-quartz veins at Dome Mine, near Porcupine, Ont. (Photo 

by the author.) 

If the stalactite and the stalagmite grow together, forming a con- 
tinuous deposit from the roof to the floor, it is called a column or pillar. 
A growth along the wall of the cave extending from the floor to the 
roof is called a pilaster. In some places this deposition goes on until 
the cave that was originally formed by the groundwater is completely 
filled by it. The more massive and compact deposits formed in the 
cave are quarried and used as onyx marble or Mexican onyx. (See 
Figs. 153 and 154.) 

239. Spring Deposits. — Calcite or carbonate of lime is 
frequently deposited around springs, which are streams of 
groundwater appearing at the surface. The deposit by the 



GROUNDWATER 



243 



spring is formed similarly to that in the cave, namely, by the 
escape of the carbonic acid gas and evaporation of some of the 
water, causing part of the dissolved lime to be deposited. It 
is frequently deposited on the surface of moss, leaves, or twigs, 




Fig. 153. — Stalagmites and stalactites in Marengo Cave, Ind. 
by W. S. Blatchley.) 



(Photo 



244 ELEMENTS OF PHYSICAL GEOGRAPHY 

because a large area is there exposed to evaporation. Such 
porous deposits are called calcareous tufa. The more massive 
deposits formed by springs and streams are called travertine, a 
name which is sometimes used for all the deposits of carbonate 




Fig. 154. — Small stalactites in Howe's Cave, N. Y. 

of lime from solution. The Coliseum and St. Peter's and many 
other large buildings at Rome are constructed of travertine, 
quarried from an extensive deposit formed by the springs at 
Bagni, near Rome. (See Figs. 106, 155, and 156.) 

Other materials than lime may be brought to the surface by the 
springs and deposited, such as iron oxide, sulphur, and silica. The 
silica-depositing springs are generally hot springs. Iron leached from 
the rocks in this way is frequently deposited in bogs and shallow lakes, 
forming bog-iron ore. 

Concretions such as claystones, clay ironstones, geodes, turtle 
stones, etc., are formed by the groundwater depositing minerals 



GROUNDWATER 



245 




Fig. 155. — Travertine deposited by hot springs on the mountain side in 
Yellowstone National Park. (Photo by U. S. Geological Survey.) 




Fig. 156. — Travertine, carbonate of lime, deposited by springs at Bagni, 
near Rome. (Photo by J. C. Branner.) 



246 ELEMENTS OF PHYSICAL GEOGRAPHY 

in more or less rounded masses in the midst of a rock of dif- 
ferent composition. Claystones consist of lime carbonate 
deposited in a bed of clay. Claystones and clay ironstones 
are formed in clays and shales. Limonite concretions are 
formed in limestones and slates. Geodes, composed generally 
of an outer shell of quartz, lined with quartz, calcite, or other 
crystals, commonly occur in limestones. Flint concretions 
occur in chalk and limestone (Fig. 157). 

240. Induration. — Mineral matter, such as silica and the 
carbonates of lime and iron, carried in solution by the ground- 
waters, is sometimes deposited in the open spaces between the 
grains in a bed of sand or gravel, cementing the particles to- 
gether and thus changing it into a bed of sandstone or con- 
glomerate. This is one of the principal ways in which beds 
of sediment are indurated or changed to solid rock. Frequently 
the water is brought to the surface by capillarity, where it 
evaporates, precipitating the mineral matter in the pores. 
The fact that many sandstones are harder on the surface of the 
outcrop than in the interior of the bed is accounted for in this 
way. The same is true of many boulders. 

In many places in the northern United States, portions of the 
glacial sand and gravel deposits are cemented by calcite deposited 
from solution in the groundwater. The student may readily test this 
by placing a piece of the material in some dilute acid and noting the 
rapid effervescence, followed by the crumbling of the piece into separate 
grains or pebbles. It is the small per cent of lime that makes the 
glacial gravels better road-making material than the gravels from the 
creek beds. 

241. Reappearance of Groundwater at the Surface. — What 
becomes of all the groundwater that sinks into the earth? 
Part of it is brought up by capillary attraction and evaporated 
from the surface in dry weather. Part of it is brought up 
through the roots and stems of plants and evaporated from the 
leaves. Part of it reaches the surface through artificial open- 



GROUNDWATER 



247 



ings, such as wells, artesian wells, mines, tunnels, and borings. 
Part of it combines chemically with minerals beneath the 




Fig. 157. — Claystone concretion made of carbonate of lime deposited by 
groundwater in shale rock. The growing concretion has bent and twisted the 
shale layers in which it was formed. (Photo by I. P. Hazard.) 

surface and is, temporarily at least, locked up as water of 
crystallization. The water of crystallization is abundant in 



248 



ELEMENTS OF PHYSICAL GEOGRAPHY 



much of the loose surface rock, in clay, and in brown iron ore. 
It may be detected by taking a handful of clay soil, drying it 
thoroughly, and putting part of it in a test tube. Heat it over 
a gas lamp, when the water of crystallization will be separated 
and condensed as drops on the side of the tube. The amount 
of water may be determined by weighing the sample before 
heating and after heating. The experiment is better performed 
with gypsum or limonite. 

Part of the groundwater penetrates the rocks to great depths 
and may not get back to the surface for many centuries ; pos- 
sibly a small part of it may never return. A considerable and 
very important part of the groundwater is returned to the 
surface through springs and seepage, including hot springs 
and geysers, and vast quantities are thrown out with the rock 
material in volcanic eruptions. 

242/ Wells. — Wells are openings dug or bored from the 
surface down to a short distance below the water table for the 
purpose of obtaining water; in the ordinary well the water 



a 
b 






\V3 


^\V2 ^yy / / 


c 




J W2 




S^^~^ jS 






^Xj?^' 



Fig. 158. — Variation of the water table with the seasons, a, temporary 
water table in wet season, water in all the wells. Water table at b, Wl is dry. 
Water table at c, dry season, W2 and Wl are dry. 



stands as high as the water table, but no higher than the 
water table. In fact, the best way to locate the water table 
in any region is by the level of the water in the wells when they 
are first opened. Sometimes excessive use of the water from a 
few large wells or many small ones may cause a lowering of the 
water table that is often of serious importance (Fig. 158). 



GRO UND WA TER 249 

Not every well opening sunk below the water table will 
prove productive; because in some places the rocks are so dense 
that very little water can find its way through into the well. 
In porous rocks the wells are fed by water which seeps through 
the pores into the well opening, and any well sunk into an 
aquifer or porous layer below the level of the water table will 
be productive. In the denser rocks the wells are fed by tiny 
underground streams. The well that strikes one or more of 
the little streamlets may have a bountiful supply of water, 
while another close by that has missed the streamlets (or so- 
called veins of water) may be barren. 

The reason that some wells go dry in times of drouth is that the 
water table sinks below the bottom of the well. Sometimes the re- 
verse is true, when the water table rises near or even to the surface 
and the well is filled to overflowing. (See Fig. 158.) 

243. Artesian Wells. — An artesian well differs from a 
common well in that it occurs only in inclined strata down the 
slope of which the groundwater moves and enters the well 
under pressure which causes it to rise above the local water 
table. The water may even flow out of the mouth of the well, 
which it does frequently with considerable force. The 
name artesian is derived from Artois, a province in France, 
where the first well of this kind was bored. It was a very strong- 
flowing well and for a long time only flowing ones were called 
artesian, but now the name is used for all deep wells where the 
water enters under pressure and rises considerably above the 
point of entrance and above the water table. (See Figs. 159, 
160, and 161.) 

The necessary conditions for an artesian well are (1) a layer 
of porous rock, the aquifer, through which the water can per- 
colate freely ; (2) the strata inclined to the horizontal ; (3) the 
porous layer outcropping in a region of considerable rainfall, 
and (4) the aquifer overlain by a layer of rock less pervious ; 



150 



ELEMENTS OF PHYSICAL GEOGRAPHY 



(5) all the strata dipping into the groundwater zone. It is im- 
material what kind of rock is below the aquifer ; if impervious 




Fig. 159. — Artesian wells, WW, in which the water enters under pressure 
from the aquifers, AAA. Conditions more favorable for good wells in middle 
and lower figures than in the upper one. 

it will hold the water above it ; if porous it will fill with water 
and in that way become impervious. (6) There should be 
no natural escape for the water between the outcrop and the 




Fig. 160. — Section from the Black Hills across portion of the Great Plains. 
The Dakota sandstone is the aquifer which carries the groundwater for many 
miles out under the Great Plains to supply hundreds of artesian wells. 



well ; nor (7) any obstruction to prevent the water reaching 
the well. (Study the diagrams, Figs. 159, 160; see Fig. 161.) 
The most favorable condition for an artesian well is a gentle 
inclination of the strata, as in Fig. 160, and not highly inclined, 



GROUNDWATER 



251 



as in upper Fig. 159, because in the latter case the well must be 
near the outcrop in order to reach the aquifer or water-bearing 
layer, while in the first case the well may be many miles distant, 




Fig. 161. — Flowing artesian well at Woonsocket, S. Dak. Itthrows a stream 
of water to a height of 97 feet. See Fig. 160. (Photo by U. S. Geological 
Survey.) 



252 ELEMENTS OF PHYSICAL GEOGRAPHY 

even in a semiarid or desert region, and yet get the water from 
the rain belt far away. Thus there are artesian wells on the 
Sahara, fed by the rainfall on the bordering mountains. The 
rain that falls on the sharp-crested foothills of the Rocky 
Mountains and the Black Hills is carried in a bed of sandstone 
out under the Great Western Plains for many miles, where it 
is obtained from artesian wells, in some places even in sufficient 
quantities for irrigation purposes. The gently inclined beds 
of clay and sand on the coastal plain of Long Island and New 
Jersey favor productive artesian wells, which might even be 
sunk out in the ocean and furnish a bountiful supply of fresh 
water. (See Figs. 161 and 276.) 

244. Springs. — Much of the groundwater returns to the 
surface in the form of springs, which are streams of groundwater 
emerging at the surface, and varying in size from the tiny trickles 
to great rivers. Silver Spring in Florida and Mammoth Spring 
in Arkansas are each large enough to float a small steamboat 
(Fig. 162). 

Sometimes the groundwater descends only a few feet below the 
surface until it finds its way back to the surface through a spring. 
Sometimes it descends thousands of feet before it is returned. 

245. Temperature of Springs. — The temporary springs fed from 
water near the surface vary in temperature during the year, becoming 
warmer in summer and cooler in winter. The permanent springs, 
however, are fed by water from below the permanent water table, 
which is generally below the zone of variable temperature, and the 
water has a uniform temperature throughout the year, generally about 
the mean annual temperature of the place. (Compare the tempera- 
ture of the water in some of the springs in your neighborhood in the 
summer and in the winter months. Why does the water seem colder 
in the summer and warmer in the winter?) Some springs in a rocky 
region have a temperature considerably below 55°, because part of the 
water comes from melting ice which accumulates in the talus slopes 
during the winter and melts slowly during the summer. Sometimes 
the ice forms in limestone caves. There are several of these caves 
in the limestone near Syracuse, New York. 



GROUNDWATER 



253 



Such cold spings should not be confused with ice caves or ice mines, 
in which the groundwater changes to ice during the warm season. The 
ice mine near Coudersport, Pennsylvania, is an excavation dug in the 




Fig. 162. — View of Silver Spring, Fla. Silver Spring is the emergence of an 
underground river and the head of Spring River. (Photo by the U. S. Geological 
Survey.) 



254 



ELEMENTS OF PHYSICAL GEOGRAPHY 



mantle rock on a hillside. Ice forms in this opening during the summer 
months, and is said to melt during the cold winter months. 

246. Hillside Springs. — Very large springs generally occur 
in the bottom of a valley. But a great many small and medium- 
sized springs emerge at different elevations on the hillsides, 
frequently a number of them at the same level. These are 




' J Silurian 



Fig. 163. — Over 40 springs emerge on an area of five square miles at Eureka 
Springs, Ark. The chert capping the hills is porous enough to permit nearly 
all the rainfall to become groundwater, which percolates down to a bed of nearly 
impervious shale, where it emerges at the outcrops in springs. 



GROUNDWATER 



255 



known as hillside springs, and are caused by the groundwater, 
in its descent from the surface, meeting a bed of clay, shale, 
or other dense rock, and following along the top of this layer 
until it emerges on the surface (Figs. 163 and 164). 

247. Seepage. — Groundwater generally collects into little 
streams on the top of the impervious layer and the emergence 
of such a stream at the surface forms a spring. Sometimes, 
however, it flows in a sheet along the entire surface of the 




>.'? >»;; ,.,» ^.y 



O^T. ,<■ 



i , \ i,i 



' > v| . . '■' .' . ' 



i " BgggS gB ? x . wnx 



! ■ '■' ■ ' ■' . . 'i^ 



T~f 



VS. ,1 ,V , V jj 






i , i , i a, y 'u , v , I A ,11' >, , it 



Fig. 164. — Vertical section through Eureka Springs, Ark. 
Compare with Fig. 163. 



dense layer, and then instead of flowing out in streams, it 
seeps or trickles out along the line of outcrop of the layer in 
sufficient quantities to keep the surface wet, frequently forming 
a swamp or bog on the hillside. This is called a seepage spring. 

Fissure Springs. — Fissure springs consist of those in which 
the water, in its underground passage, enters a fissure or crack 
leading to the surface, through which the water emerges under 
hydrostatic pressure, as in the artesian well. 

248. Mineral Springs. — All spring water contains some 
mineral matter in solution, but certain ones, known as mineral 
springs, are characterized by an excessive amount of some 
common mineral matter, as carbonate of lime, carbonate of 
iron, or hydrogen sulphide, or by the presence of some rare 
compounds, like those of lithium. The most common mineral 
springs are the lime, sulphur, iron (chalybeate), magnesia, 
carbonic acid, potash, soda, lithia, and silica springs. 



256 ELEMENTS OF PHYSICAL GEOGRAPHY 

Some of the mineral springs are hot and others are cold. 
Some have a wide reputation for the curative properties of 
the water, for the benefit of which people travel long distances. 
In some places the waters are bottled and shipped to distant 
points. What mineral springs can you name in your own 
state ? Make a list of the places and the kind of springs. The 
springs shown in Fig. 163 are widely known mineral springs. 
There are many mineral springs in the Rocky Mountains and 
in the Sierra Nevada Cascade range of the West. Some of 
the most famous are those at Manitou, Colorado, Hot Springs, 
Arkansas, Saratoga Springs, New York, and French Lick, 
Indiana. 

249. Hot Springs. — The water in some springs has a high 
temperature, sometimes at or near the boiling point. Some 
hot springs occur in the region of active or extinct volcanoes, 
where the rocks have not yet cooled from the former highly 
heated ' condition. The circulating groundwaters come in con- 
tact with these heated rocks below the surface, are warmed, 
and emerge as hot water. 

In some places, where hot springs are remote from any 
volcanic rocks, they may be caused (1) by intrusive molten 
rocks which have not reached the surface ; or (2) by heat pro- 
duced by friction in the bending and fracturing of the rocks 
in the folding of the mountains ; or (3) by chemical action go- 
ing on in the rocks through which the water is passing. Hot 
springs are found in mountainous countries, in Arkansas, 
Virginia, South Dakota, and many of the Rocky Mountain 
and Pacific states. 

250. Geysers. — Geysers are boiling hot springs that erupt 
intermittently. The water and steam are thrown out periodi- 
cally, sometimes to a height of several hundred feet. The 
eruptions take place in some geysers at quite regular intervals, 
while in others the intervals are very irregular, sometimes 
several hours or several days, or even years. (Fig. 165.) 



GROUNDWATER 



257 



The water in all geysers contains alkali (soda or potash) in solution, 
which in turn dissolves silica in the deeper portions of the circulation. 
When the heated silica-bearing waters approach the surface, the de- 
crease in pressure and loss of temperature causes some of the silica 




Fig. 165. 



Old Faithful Geyser during an eruption. Yellowstone National 
Park. (Photo by U. S. Geological Survey.) 



258 ELEMENTS OF PHYSICAL GEOGRAPHY 

to be deposited along the sides of the opening, making a smooth but 
crooked and irregular tube through which the water finds its way to 
the surface. The deposit formed on the surface by the geyser waters 
is siliceous sinter, a variety of quartz, sometimes called geyserite. 

251. Geyser Eruptions. — The eruption of the geyser is 
caused by the high temperature in the deeper portions of the 
tube, which causes the water to be heated above the boiling 
point. A portion of.it finally changes to steam, the expansion 
of which lifts the plug of water in the upper part of the tube, 
causing it to overflow and thus release the pressure on the water 
towards the bottom. This release of pressure permits a large 
volume of steam to form suddenly, and forcibly expel all the 
water from the tube (Fig. 165). The water partially cooled 
in the air runs back, fills up the tube, and stands until the 
bottom is again heated above the critical point, that is, the 
point where the water will change to steam under the existing 
pressure, when another eruption takes place. The critical 
point where water changes to steam at sea level on the surface 
of the earth is 212° F., but deep beneath the surface under the 
increase of pressure it may reach a temperature of 250° or more 
before it forms steam. Another possible explanation for some 
of the geysers is that steam accumulates in an underground 
cavity until it has sufficient force to overcome the resistance of 
the column of water, when it violently expels the water from the 
opening. 

The constant loss of heat from the eruptions of hot water causes a 
decrease in the activity of the geyser, which in time becomes a hot 
spring, and finally a cold spring. In the Yellowstone Park there are 
about 3000 openings, some of which are geysers, but the majority of 
which are now springs, some hot and others cold. A decrease in the 
activity of some of the geysers has been noted in the past few decades. 
Even "Old Faithful," which formerly erupted regularly every hour, 
is now becoming irregular, with sometimes an interval of an hour and 
a half between eruptions. The decrease in activity of some of the 
geysers is balanced, in part at least, by increased activity in others. 



GROUNDWATER 259 

At present there are four geyser localities known in the world ; one 
in Yellowstone National Park in Wyoming, one in Iceland, one in New 
Zealand, and one in South America near the headwaters of the Amazon. 
The "Valley of Ten Thousand Smokes," in Alaska, contains many 
hot springs and thousands of steam and gas vents, but no geysers. 

It is thought that this represents an early stage of a geyser region ; as 
the rocks become cooled to greater depths, many of the present steam 
vents will become geysers. A further study of this interesting locality 
is expected to throw light on the early history of Yellowstone Park and 
other geyser regions. 

252. Soil Water. — The soil and the other mantle rock above 
the water table contain some water. The amount varies in 
different soils and in the same soil from time to time. It is 
most abundant during and immediately following rains and 
least at the end of a long dry season. The rain water per- 
colates through the pore spaces in the soil so slowly that some 
of it remains many days after the rain. In fact some of it is 
held in the soil by the force of capillarity and surface tension 
of soil particles. In addition there is always more or less 
hygroscopic water derived from the air in the pore spaces. A 
fraction of all soils consists of a jelly-like substance known as 
colloids, in which the water forms a jelly with the earthy ma- 
terial. 

The soil water in the form of the colloids, hygroscopic and 
capillary water, and free water is essential for the growth of 
food crops. Some water-loving plants can grow with their 
roots below the water table, but most of our food crops would 
die, that is would drown, if their roots were buried in water too 
long. The roots of food plants need air as well as water. 

The soil water not only furnishes drink to the plants, but it 
also furnishes part of the plant food. The growing plants use 
up the soil water in large quantities, and if there is no re- 
newal of the supply, after a time the plant withers and dies. 
The loss of soil water is most rapid near the surface so that 
plants with short roots are the first to die and plants with long 



260 ELEMENTS OF PHYSICAL GEOGRAPHY 

tap roots, like sweet clover, withstand the drouth much longer 
than short-rooted plants. Where the water table is near the 
surface the water, in rising from it by capillary attraction, often 
supports the plant growth through long intervals of dry weather. 

In humid regions the farm crops are supplied with ground- 
water through the growing season by the summer rains. In 
semiarid regions the growth is facilitated by the special methods 
of dry farming. 

253. Irrigation. — In arid regions where the precipitation 
is too light to supply sufficient soil water, irrigation is used to 
supply the deficiency. By means of irrigation the water supply 
can be regulated to the needs of the plant, and has proven 
so successful that it is now being used in humid regions, to pre- 
vent the loss which frequently occurs in periods of drouth. 
It has been found especially useful in vegetable gardening. 

In the arid and semiarid lands of the West special methods 
of dry farming and large irrigation projects have been the means 
of reclaiming vast areas of formerly waste lands which now 
produce bountiful crops. (Fig. 166.) 

One of the principles of dry farming is frequent cultivation to keep 
the surface loose and friable and thus check evaporation. When the 
surface bakes or forms a crust, evaporation increases, which means a 
loss of soil water needed by the plant roots. 

QUESTIONS 

1. What becomes of the water that is evaporated from the ocean? 

2. Why does groundwater move faster through sandstone than 
through clay beds? 

3. What kind of rock material underlies swamps and bogs ? 

4. Why do ditches and tile drains improve clay lands for farming 
purposes ? 

5. Many swamp-land areas that were formerly waste land are now 
(after draining) more valuable than surrounding dry-land areas. Why? 

6. Why are wells dug deeper on the uplands than on the lowlands ? 

7. If you should dig a well near the seashore would the water in it 
be fresh or salt ? Why ? 



GROUNDWATER 



261 




Fig. 166. — Map showing the location of the large government irri- 
gation projects. 



262 ELEMENTS OF PHYSICAL GEOGRAPHY 

8. A well near a lake shore gets water from the land, not from the 
lake. Would the surface of the water in such a well be higher or lower 
than the surface of the lake? 

9. Many small lakes in northern United States have no streams 
flowing into them. Where does the water come from ? 

10. What is an aquifer? What kinds of rocks make the best 
aquifers ? 

11. Many wells become dry in times of drouth. Why? 

12. Why are there generally more caves and cavities in limestones 
than in shales and sandstones ? 

13. Why are there more caves on the hillsides and uplands than 
in valleys or low plains ? 

14. In the waters in some caves there are blind fish. How do you 
account for them ? Why are they not in all eaves ? 

15. Explain the different kinds of natural bridges. Give examples. 

16. How do gangue minerals differ from ores ? 

17. Write a list of all the ores you have seen and add to it all others 
you know about. 

18. Name the minerals that act as a cement in changing sand to 
sandstone. 

19. Place a spoonful of water on a saucer or dish and place on it a 
lump of loaf sugar. What becomes of the water? Would the same 
thing happen with a lump of soil ? Try it. 

20. Explain the difference between an artesian well and a common 
well. 

21. Why are there so many artesian wells on the Atlantic Coastal 
Plain and on the Great Western Plains ? 

22. Name and locate the mineral springs you have seen. 

. 23. What kinds of mineral springs are also medicinal springs ? 

24. What causes hot springs? Why are they found mostly in 
mountainous regions? 

25. Are geysers mineral springs? Are they medicinal springs? 
What minerals do they contain ? 

26. Why is soil water necessary for plant growth? 

27. Why is frequent cultivation of the soil more important for 
plant growth in dry regions than in humid ones? 



CHAPTER VIII 
RIVERS 

Weathering of rocks is the first step in the process of erosion 
of the land areas. The next step is the moving of this loose 
material down the slopes towards the sea. Some of the material 
is transported by the winds, as described in Chapter II ; some 
of it by gravity, as mentioned in Chapter IV ; in some mountain- 
ous regions, glaciers carry large quantities of rock material to 
lower levels ; but most of the transporting work is done by the 
rain that falls on the surface and runs off through the streams. 

254. River Valleys. — Much of the rain that falls on the 
earth runs down the slopes, washing out depressions through 
which the water flows to the sea. It is the run-off of the rain 
water that carries with it the loose material of the mantle rock. 
The water flowing down the slope gathers in the depressions, 
wearing them deeper and wider, thus forming gullies, ravines, 
and valleys. The larger these depressions become the more 
water gathers in them ; the more water the faster it flows and 
the more mantle rock it carries away, thus deepening and widen- 
ing the valleys (Fig. 167). Each gully and valley so formed 
makes additional slopes on which new gullies and other valleys 
form. By following down one of the valleys one finds it joined 
by other valleys and still others, the main valley increasing 
in size with each additional tributary. The groundwater 
that emerges in springs and seepage joins the direct run-off 
of the rains and melting snows, increasing the volume of water 
in the streams in flood season and keeping up the flow of the 
streams in the dry season. 

263 



264 ELEMENTS OF PHYSICAL GEOGRAPHY 

By watching the formation and growth of a gully on a hillside 
during a heavy rain, one can see that the larger the gully becomes 
the faster it increases in size, and as this goes on year after year, age 
after age, the depression increases- in depth and length and width 
until a river valley is the result. Many of the river valleys are formed 
in this way. Most large river valleys have a more complicated his- 




Fig. 167. — Gullies forming on a deforested hillside, North Carolina. (Photo 
by U. S. Geological Survey.) 

tory than that just outlined, due to the irregularities and changes 
in the land areas over which they extend. River valleys are for the 
most part depressions in a land area formed by the waters flowing 
over the area (Fig. 168). 

In general the largest streams flow in the largest valleys, and most 
of the valleys widen as one follows downstream and become narrower 
as one follows upstream, generally terminating in a gully or a series 
of gullies. 

Valleys that extend across rocks of different degrees of hardness 
are wider in the soft rocks, which are eroded more rapidly, and narrower 
in the hard rocks, where erosion is slower. 



RIVERS 



265 



255. River Basin, Valley, and Channel. — The terms river 
basin, valley, and channel should not be confused. A river 
basin is all the land from which the rainfall drains into the 
river. A valley is the depression in the basin through which 
the river runs and which was formed by the river and other 




Fig. 168. — Gullies in a semiarid region, formed by the run-off of the rain- 
fall, Big Bad Lands, S. Dak. (Photo by U. S. Geological Survey.) 



agencies of erosion. The channel is the depression in the floor 
of the valley occupied by the water at ordinary high-water 

stage. 

The Mississippi Basin includes all the land drained by the Mis- 
sissippi River and all its tributaries, extending from the water divide 
on the Rocky Mountains to the divide on the Appalachian Mountains, 
and south of the water divide between it and the St. Lawrence Basin 
and that of the Red River of the North, and comprising an area of 
mora than one and one-fourth million square miles. 



266 



ELEMENTS OF PHYSICAL GEOGRAPHY 



The Mississippi Valley is the depression cut by the river east of the 
middle of the basin. The valley varies in width from a few miles in 
its upper course to fifty or more in its lower part. Near St. Louis 
it is ten miles wide. At Memphis and Vicksburg it is thirty-five 
miles wide. 




Fig. 169. 



— Stream degrading or wearing down its channel in very hard 
rock in Ausable Chasm, N. Y. (Photo by the author.) 



The Mississippi channel is the depression occupied by the river in 
the bottom of the valley. The channel is the depression between 
the river banks. The valley is the depression between the tops of the 
river bluffs. The basin is the depression between the water divides 
on the bordering mountains. 

256. Growth of River Valleys. — Most river valleys are 
growing larger by deepening, widening, and lengthening. The 
valley is deepened by the river carrying away the loose material 
in the channel and grinding away the bed rock. Such a stream 
is said to be degrading, or wearing its channel deeper (Fig. 
169). The newly formed gully is degrading along its whole 



RIVERS 



267 



length, but in the larger and older streams the channel is being 
cut down or degraded in some places and temporarily filled 
up or aggraded in others (Fig. 170), owing to the differences 
in the hardness of the rocks and the slope of the channel. The 
limit to the deepening of any valley is its base level. The lower 
end of nearly all valleys has reached this depth limit, but as 




Fig. 170. — Stream aggrading, or building up its channel. Uncompaghre 
Creek, Ouray, Colo., just below the canyon. (Photo by the author.) 



one follows up the valley he finds the stream cutting down 
and deepening the valley on all the steeper parts of the course, 
the deepening going on most rapidly towards the head of the 
stream, where the velocity is greatest. 

257. Graded Valleys and Base Level. — The portion of a 
valley where the down-cutting has stopped is said to be graded ; 
or if deposition is going on, it is below grade. The lower portion 
of nearly all the larger valleys is graded. There are also many 



268 ELEMENTS OF PHYSICAL GEOGRAPHY 

stretches of varying length all along the course of any valley 
that are temporarily graded. Such portions are called reaches, 
pools, or dead water (Fig. 171). Mill ponds, reservoirs, lakes, 
and swamps occur on such temporary grades or below grade. 
The cutting on the rapids and the deposition on the reaches con- 
tinue until both have a uniform grade. The process continues 
until the stream has one uniform grade from end to end and no 




Fig. 171. — Reach and rapids on Onondaga Creek, N. Y. (Photo by 
C. S. Wheelock.) 

portion of the valley is being either degraded or aggraded. 
The stream has then reached base level. Very few rivers ever 
reach this stage, but it is the end towards which all are working. 

A stream has reached base level when it is completely graded 
and mechanical erosion has ceased. Its work has been done. 
There are no steep slopes, hence no hills or elevations, but a uni- 
form plain with just slope enough for the water to run off with- 
out enough velocity to carry any sediment. 

Profile of a River. — A line representing the slope of a river's 
channel from the headwaters to the mouth of the river is called 
a profile of a river. It represents the slope of the channel or the 



RIVERS 



269 



inclination of the bed to the horizontal. It is one of the chief 
factors in determining the velocity of a stream. In the ac- 
companying profiles of the Hudson and Mohawk rivers notice 
how steep the upper Hudson is compared with the Mohawk 
and the lower Hudson. The upper Hudson has many rapids 









































LA 


KETf 


ARC 


FTH 


:clo 


UDS 




















































ft/ 




























































o 














Li 

u 


/ 










U 
Cfl 














u 

z 


L 










Id 

z 








s- 








o 

■OS 






z 




1 


ludsor 


R 




O 

OS ~- 






















hawk 



Fig. 172. — Profiles of the Hudson and Mohawk rivers. 

and falls. Compare the profiles of a number of large rivers. 
(See Bulletin No. 44 of the Water Supply and Irrigation Papers 
published by the United States Geological Survey ; see also 
Fig. 172.) 

258. Widening of Valleys. — As soon as a valley is started 
it begins to widen. Rain wash on the sides of the valley, 
assisted by weathering and gravity, carries material to the 
bottom, where it is swept away by the stream. If the 
velocity of the stream is sufficient to cut down much faster than 
the material is washed down the sides, the valley deepens 
faster than it widens. If the down-cutting is in hard rocks, 
with little wash from the sides, it forms canyons with vertical 



270 ELEMENTS OF PHYSICAL GEOGRAPHY 

walls. In softer rocks or with slower down-cutting the tops 
of the valley walls crumble away and the valley becomes 
V-shaped in cross section. When the stream reaches tem- 
porary or permanent grade and ceases to cut down its channel, 
the widening of the valley continues, flats form on the bottom, 
and the cross section of the valley becomes U-shaped. 

In all such cases the widening of the valley goes on faster in humid 
regions, where the weathering is more rapid, than in the dry climates. 
The widening of the valley continues until the top of the valley wall 
reaches a slope in the opposite direction, where a sharp ridge or divide 
is formed and widening ceases. 

259. Flood Plains. — The flat area in the bottom of the 
valley, which the water overflows in flood season, is called a 
flood plain. As the flood waters subside a deposit of sediment 
is left on the plain. This continued year after year builds up 
the level of the plain and renews the fertility of the soil. Hence, 
flood plains are always covered with a great thickness of rich 
soil. 

On some large rivers, like the Mississippi, the Nile, the Hoang 
Ho of China, the flood plains are large, covering thousands of 
square miles. Because of the productive soil they support 
a dense population. The exceptionally high floods often prove 
destructive to property and life on these plains. 

In general the flood plain area becomes narrower as one ascends 
a river, and in the upper courses of the stream, in the narrower valleys 
in the hill country, the flood plain areas, commonly known as "bottom 
lands," are confined largely to the inside of the curves or bends of the 
river, with steep bluffs on the opposite side of the river on the out- 
side of the bends. Flood plains of this kind occur along the Sus- 
quehanna River in southern New York and northern Pennsylvania, 
and along the upper Ohio River from Pittsburgh to Cincinnati. 

There are no large flood plains on the Hudson or the Niagara 
Rivers. Why ? 

260. Meanders. — When a river has graded a portion of its 
course and formed a flood plain, it ceases to corrade the bottom 



RIVERS 



271 



of its channel at that place, but continues to cut at the sides or 
banks. Where the current is deflected to one side it cuts away 
the bank at that point, producing a curve which deflects the 
current across to the opposite bank below, where another curve 
is formed (Figs. 173 and 174). In both places the bank is worn 
away and the stream in time becomes quite crooked or meander- 




Fig. 173. 



Crooked Creek, Calif., meandering on a narrow flood plain. 
(Photo by U. S. Geological Survey.) 



ing. While the stream is cutting the outside of the meander 
curve, sand and gravel are being deposited on the inside of the 
curve (Why? Study the diagrams) and the whole channel is 
gradually shifted into or even across its flood plain. The 
meander curve once started continues to increase its curvature 
until the stream cuts across the neck between two approaching 
curves and thus straightens that portion of the channel. The 
cut-off is gradually silted up at the ends, forming first a lagoon 



272 



ELEMENTS OF PHYSICAL GEOGRAPHY 



and later on an oxbow lake. These oxbow cut-offs, so common 
on the flood plains of large rivers, may frequently be observed 




Fig. 174. — Coal Creek meandering on the Laramie Plains, Wyo. (Photo by 

U. G. Cornell.) 

on small brooks where they are following a winding course 
through a meadow. (Study the Mississippi River maps, and 
Figs. 175, 176, and 177.) 




Fig. 175. — Development of river meanders. A cut-off forming at C. A 
cut-off at D has formed the oxbow lake, LL. 



RIVERS 273 

When the meander curve reaches the outer limit of the flood 
plain of the river, it begins to undercut the river bluff and thus 
widen the valley. (Suggestion to the teacher: Take the 
pupils to meander curves on near-by streams. Take photo- 
graphs each year for use with succeeding classes so that they 
can see the changes.) (See Fig. 176.) 




Fig. 176. — A cut-off forming an oxbow lake on the Frazer River in Middle 
Park, Colo. (Photo by the author.) 



261. Lengthening of Valleys. — Valleys grow longer in 
several ways. One way is by erosion at the head of the terminal 
gully (Fig. 178). This growth continues as long as there is 
any undrained or poorly drained land at the head. It ceases 
when the head of the valley meets the head or side of another 
valley where the surface slopes in the opposite direction. This 
is the divide which limits the length of the valley. As it grows 



274 ELEMENTS OF PHYSICAL GEOGRAPHY 

in length the head of one valley sometimes reaches the lower 
end of another and the two become one (Fig. 178). 

262. Stream Energy. — Every drop of water above the level 
of the sea contains a certain amount of energy. In a stream 
channel the energy is expended in (1) carrying sediment, 
(2) corrasion or wearing away the rocks over which it flows, 



Fig. 177. — Oxbow lakes on the lower Mississippi River. Notice the deposi- 
tion on inside of curves at a a a a. 

and (3) velocity. All the energy of a stream may be expended 
in velocity, as it is in clear streams. If sediment is added to the 
clear stream, the velocity is checked, as part of the energy is used 
up in carrying the load. If only a limited quantity of sediment is 
carried, part of the energy is used in eroding the rocks over which 



RIVERS 275 

the stream flows. If more and more sediment is added, there 
comes a time when the work of erosion ceases, as all the energy 
is used in carrying the sediment. If still more sediment is added 
the stream ceases to flow, until some of the load is deposited. 



. 








W "*- 














SShbHh 



Fig. 178. — Gully in California lengthening by head erosion and widening by 
slumping at the sides. (Photo by U. S. Geological Survey.) 

A boy can run fast with one brick, but put ten bricks in his arms 
and he cannot run so fast. Add ten or twenty more and he cannot 
run at all until he drops some of them. Energy can be distributed, 
part of it used in one "way, part in another, but the same energy cannot 
be used in two ways at the same time. 

263. Corrasion. — Corrasion is the wear of the rocks in the 
stream channel and is done by the sand, mud, and rock 
fragments carried by the stream. Clear water does not corrade 
or wear away hard rock. The rock fragments carried by the 
stream are the tools used by the water to corrade the hard 
rock. If the velocity of a corrading stream is doubled, the 
corrading power of the stream is increased four times, because 



276 ELEMENTS OF PHYSICAL GEOGRAPHY 




Fig. 



179. — Chittenango Falls, N. Y. Cascade type of falls over layers of 
hard limestone. (Photo by C. S. Wheelock.) 



RIVERS 



277 



in a given time twice the number of particles will strike the 
corraded surface with twice the former velocity. Hence the 
corrading power of a stream increases as the square of the increase 
in velocity. This is the law of corrasion. 




Fig. 180. — Rapids at R change to falls at F and F 1 , and again change to 

falls at R 1 . 

The rate of erosion varies with the hardness of the rock. As the 
rocks vary in hardness from place to place, the softer parts wear away 
first, which produces irregularities in the channel. In many places 
this produces rapids on the hard rocks and pools or reaches on the 
softer rocks. In some places it causes waterfalls or cataracts (Fig. 179). 

264. Waterfalls. — Rapids ' change to waterfalls in a stream 
channel where the stream flows across the edge of a hard layer 
of rock in the midst of softer layers. (See Figs. 180 and 181.) 




Fig. 181. — Rapids changing to falls on Bog River, N. Y. 



278 



ELEMENTS OF PHYSICAL GEOGRAPHY 



If the hard layer is vertical the falls in time are worn down to 
rapids, which in time are graded and then disappear. If the 
hard layer is inclined upstream or is horizontal, the falls recede 
upstream, first increasing in height, then decreasing until they 
again change to rapids. If the strata incline or dip downstream 




Fig. 182. 



Niagara Falls, on the Niagara River, N. Y. 
waterfalls in the United States. 



The most famous 



at an angle equal to or greater than the slope of the channel, 
falls are not formed (Fig. 181). 

Most of the high waterfalls occur where some other agency 
than the stream has worn away the rocks below the falls so that 
a stream flowing over a hard layer of rock drops over a cliff 
or precipice to a lower level. Such is the case at Niagara 
Falls and scores of other waterfalls in the northern United 
States. These falls were formed at the close of the glacial 



RIVERS 



279 



period. When the ice of the glacier melted away, many of the 
old preglacial valleys were filled with materials left by the melt- 
ing ice, and the new postglacial streams flowing from the uplands 
ran. over cliffs, forming waterfalls. 

In a region which has not been worn by glaciers the main 
stream sometimes cuts down faster than the tributaries, on 
which the waterfalls occur where they flow over the edge of 
a layer of hard rock. Water- 
falls are of frequent occurrence 
on streams flowing down steep 
slopes on the mountainside and 
on canyon streams in plateaus. 

265. Niagara Falls. — Niag- 
ara Falls is the largest cataract 
in the United States and one of 
the largest in the world. There 
are other higher falls, but no 
other in the United States on so 
large a river as the Niagara 
(Fig. 182). _ 

The Niagara River was 
formed by the overflow of Lake 
Erie . As the water flowed north 
over the Erie plain it fell over 
the cliff at Lewiston at what is 
now the lower end of the Niagara gorge, where the falls were 
first formed. The surface rock at the falls is a hard limestone 
underlaid by softer shales and sandstone. As. the softer rocks 
at the base of the cliff are worn away, the overhanging hard 
rock breaks down ; this is the continuation of the process which 
caused the recession of the falls from Lewiston to the present 
location, leaving the Niagara gorge (Fig. 183). 

The falls have been moving upstream since 1842 at the rate 
of about five feet per year. If they have been receding at the 




Fig. 183. — Vertical section at Ni- 
agara Falls. The softer shales under- 
neath are worn away by the water. 
The overlying hard limestone breaks 
off and is carried down the gorge. 
The repetition of this process causes 
a recession of the falls and lengthen- 
ing of the gorge. (Drawing by 
Gilbert.) 



280 



ELEMENTS OF PHYSICAL GEOGRAPHY 



same rate since they were first formed at Lewiston seven miles 
below, they are now about 7000 years old. There are reasons 
for believing that part of the time they did not move so fast, 
and their age has been estimated at 30,000 to 50,000 years. 
If they should continue to recede at the present rate, how long 
would it be before they reach and lower the level of Lake Erie? 
There are several reasons why they probably will not move 




Fig. 184. — Falls in Watkins Glen, N. Y. (Photo by the author.) 

back as fast as they have been moving. Can you state any 
of the reasons ? Since the limestone rock at the top of Niagara 
Falls dips under the bed of Lake Erie, will the falls ever reach 
the lake? 

There are many falls of the same type as Niagara, such as the 
falls at Rochester, New York, and the beautiful Minnehaha 
Falls on the Minnesota River. 

266. Other Types of Waterfalls. — There are several other types 
of waterfalls (See Figs. 179, 146), only a few of which can be men- 



RIVERS 



281 



tioned here. Compare the falls you have seen with these and deter- 
mine to which type they belong. 

267. Montour Falls. — Montour Falls, near Watkins Glen, New 
York, do not recede in the same manner as Niagara. These falls form 
a cascade over a prominence in the channel and do not undermine 
and wear away the rock at the base. On each side of the falls, the 
weathering agencies, chiefly frost, are forming depressions, into one 




Fig. 185. — Stonequarry Falls, N. Y. Water protects the rocks over which 
it is flowing, but weathering agencies, chiefly frost, cause extension of the gorge 
at side of the falls. (Photo by the author.) 



of which the stream will in time be turned and a gorge formed. These 
falls are probably as old as Niagara and yet the gorge has hardly 
started (Fig. 184). 

268. Stonequarry Falls. — Stonequarry Falls, near Manlius, New 
York, belong to the same type as Montour Falls, but they have formed 
a gorge nearly a quarter of a mile long. Unlike the Niagara, this 
gorge is several times wider than the stream (Fig. 185). 

269. Yellowstone Falls. — The lower falls of the Yellowstone 
River in Yellowstone Park belong to a different type. Here the hard 



282 



ELEMENTS OF PHYSICAL GEOGRAPHY 



layer that causes the falls is vertical, and the falls are not receding at all. 
The beautiful canyon below the falls has been eroded by the river 
in softer rocks. The falls are sinking down in the canyon by the 




Fig. 186. 



Yellowstone Falls, Yellowstone National Park, and part of the 
canyon below the falls. (Photo by B. W. Clark.) 



slow wearing away of the hard rock, but they do not recede. They 
have been at the same place since they were first formed (Figs. 
186 and 187). 




* *V?sf8 Lower Falls 



* 3".y£' 






^im 



Fig. 187. — Section at Yellowstone Falls. The vertical position of the 
(shaded) hard layers prevents a recession of the falls. The canyon below 
the falls was formed by the stream cutting down in the softer rocks. 

270. Trick Falls. — Trick Falls on Two Medicine River in 
Glacier National Park is different from any of these. Here 
the falls are on a heavy bed of limestone that forms the entire 



RIVERS 



283 



cliff. Some distance up the river from the falls the water has 
made an opening in the bottom of the channel, through which 
it flows, emerging near the base of the falls. In extreme low 
water all the water of the river flows through the lower channel 
and there is no waterfall. In time the lower channel will be 
enlarged sufficiently to carry all the water even in flood season, 
and the present Trick Falls will disappear or rather move back 




Fig. 188. — Potholes formed on the rapids in the Big Gunpowder River, Calif. 

to the new position, where the water is now sinking in the bottom 
of the channel, and the rock between the present and the future 
falls will form a natural bridge in the valley. Natural Bridge 
in Virginia was formed in this way. (See Fig. 146.) 

271. Potholes. — Pot-shaped depressions occur, worn in 
the hard rocks by the eddies in the rapids. They frequently 
occur in the rapids just above a waterfall. In the eddies the 
swirling circular movement of the water carries around the 
pebbles and sand at the bottom, causing them to grind away 



284 



ELEMENTS OF PHYSICAL GEOGRAPHY 



the rock over which they move. These potholes vary in size from 
an inch or so to 50 feet or more in diameter, depending on the 
size of the eddy, and from a few inches to several feet deep, 
depending on the hardness of the rock and the length of time 
in which the eddy has been in existence. Similar but generally 




Fig. 189. — Large pothole formed in the limestone in the channel of th; Hudson 
River, near Glens Falls. (Photo by S. R. Stoddard.) 



larger potholes are formed by streams falling through a crevasse 
in a glacier. These are called glacial potholes (Figs. 188 and 
189). 

272. Transporting Power of Streams. — The destructive 
work of streams in flood season is well known, but the cause 
is not so commonly recognized. The carrying power of a stream 
increases as the sixth power of the increase in velocity, that is, 
doubling the velocity increases the carrying power 64 times. 
Increasing the velocity ten times increases the carrying power 



RIVERS 



285 



a million times. This is the law of transportation (Fig. 190). 
Increase in volume causes rapid increase in velocity. In the 
great Johnstown, Pennsylvania, flood in 1889 there was enor- 
mous destruction of property. Houses, freight cars, even 
locomotives were swept along in the flood of waters. Flood 
waters in the Amazon River frequently carry away acres of 
forest land along the banks of the stream. There is scarcely 
any limit to the power of water in great floods, caused by in- 
creased velocity with greater volume of water. 




Fig. 190. — A stream able to move block B has its velocity doubled, then on 
each face the size of B there will be twice as much water, each particle striking 
with twice the force, which would move 4 B. On a face 16 times as large as B 
there would be 16 times as much water with 4 times the force, which would 
move 64 B. 64 is the sixth power of 2. 



273. Flood Destruction. — The great destruction at Dayton, 
Ohio, and other cities along the Miami River during the flood in 1913 
is another striking example on a large scale of what is taking place 
along every stream, large and small, during flood season. The people 
of Miami Valley aim to prevent future disaster by constructing great 
reservoirs to hold the flood waters and permit them to run off slowly. 
Similar projects are under consideration for many of the tributaries 
of the Mississippi and other rivers, to prevent disastrous floods on 
the lower courses of the rivers. This plan has other advantages, 
such as furnishing power plants to conserve the coal supply; saving 
great quantities of valuable soil that is now being carried to the sea; 
aiding, navigation on the larger streams, etc. 



286 



ELEMENTS OF PHYSICAL GEOGRAPHY 



274. How Streams Transport Material. — Streams trans- 
port material (1) as mud and sand in suspension, (2) by pushing 
and rolling the coarser materials along the bottom, (3) by float- 
ing vegetation, ice, and dry sand, (4) in solution. 

(1) The finest sediment is carried farthest in suspension 
because it sinks more slowly. It should be kept in mind, 
however, that velocity does not destroy gravitation. Sedi- 
ment sinks just as fast in swift water as in still water, but the 




Fig. 191. — Boulders in the channel of the Potomac River in the Allegheny 
Mountains in Maryland. (Photo by Maryland Geological Survey.) 



upward currents in a river keep moving the material towards 
the surface. Hence, while the sediment is constantly sinking 
from gravity it is being elevated by the upward currents of the 
turbulent stream. 

(2) On the upper course of the river, where the slope is steep 
and the velocity great, large boulders are rolled along the 
bottom. Further down on the gentler slopes smaller boulders 
and pebbles are pushed along. On the flat plains of the lower 
valley sand is rolled along the bottom of the stream (Fig. 191). 



RIVERS 287 

(3) Dry sand will float for some distance on the surface of 
the water before it becomes wet and sinks. Large quantities 
of vegetable matter floating on the surface of a river often 
carry more or less mud and sand attached to it. In cold 
climates the ice blocks borne away on the spring floods often 
carry rock fragments and earth frozen into the ice. 

(4) The material in solution is the invisible part of the load 
which a river carries. It consists of the compounds of lime, 
magnesia, iron, soda, potash, and other substances dissolved 
from the rocks. This part of the work goes on continuously 
through the year, while the visible load is almost all carried 
during the stage of high water. Most streams, especially 
those in the hills and mountains, become clear during low. water 
and carry almost no sediment, but the material in solution by 
the springs and seepage from groundwater goes on continuously. 

275. Amount of Rock Material Carried by Rivers. — The 
total amount of material transported by rivers is almost beyond 
comprehension. From many careful measurements made dur- 
ing all seasons of the year, it has been estimated that the Mis- 
sissippi River carries into the Gulf of Mexico each year 400 
million tons of sediment and 120 million tons more in solution. 
It would require not less than 13,000,000 freight cars, each 
carrying 40 tons, to transport this material. But this is only 
a fraction of the amount of rock material transported variable 
distances by the upper Mississippi River and its many tribu- 
taries over the great basin, since only a small part of the material 
washed from the mountains and hills in a year reaches the lower 
Mississippi. 

All the other rivers of the world together transport probably 
40 or 50 times as much as the Mississippi River. 

The consideration of such figures helps the mind better to realize 
and appreciate the tremendous work of the rivers. When one con- 
siders that this work has been going on year after year through the 
long, long ages of time, he is able to grasp the idea that hUls, moun- 



288 ELEMENTS OF PHYSICAL GEOGRAPHY 

tains, and plateaus are carried away, and that if new mountains and 
new lands were not formed at different periods, it would be only a 
question of time until all highlands would be worn down to base level 
and all the rock material composing them carried to the sea. 

276. Deposits Formed by Rivers. — We are now ready to 
consider another phase of the river's work. We have learned 
that the rivers transport great quantities of rock material in 
the form of mud, sand, pebbles, and boulders. What does it 
do with them? Vast quantities are carried to the sea, but not 
all the material carried by the torrent down the hillside goes 
directly to the sea. It stops many times along the way. 

Iron from the ore mined in the hills of Minnesota goes to the battle- 
fields of Europe, but it stops at many places along the way. It stops 
on the docks at Duluth, again on the docks at Conneaut or some 
other point on the lower lakes, again at the furnace at Braddock or 
elsewhere, again in the steel mills, again at New York or some other 
seaport, then at some port across the ocean, possibly at several other 
points, before it reaches the battlefield. 

Rock material washed from the hillsides in Pennsylvania or Mon- 
tana may stop a hundred or a thousand times before it reaches the 
mouth of the Mississippi. It is too long a story to follow it through all 
the stops, but let us consider some of the places where it is deposited 
in large quantities. 

277. Increase and Decrease of Transportation. — The law 

of transportation by rivers (Sec. 272) is that the transporting 
power of streams increases as the sixth power of the increase 
in velocity. The reverse is also true. The carrying power de- 
creases at the same rate. Hence, any decrease in the velocity 
of a stream laden with sediment will cause a deposit of some 
of the load ; a sudden check causes a large deposit. 

A check in velocity is caused (1) by a decrease in gradient, (2) 

. by loss in volume, (3) by flowing into a body of standing water, 

(4) on the inside of bends in the channel, (5) by the meeting 

of cross currents in a channel, (6) by some obstruction in the 

channel, (7) by the overflow from the channel to the flood plain. 



RIVERS 



289 



278. Alluvial Fan. — A stream flowing from the hills or 
mountains out on a valley floor or plain of any kind meets a 
sudden check in velocity and deposits a large part of its burden, 
building up an alluvial fan (Fig. 192), Fans are formed in 
large numbers at the base of every steep hillside after a heavy 




Fig. 192. — Alluvial fan formed by a mountain torrent where it emerges from 
the mountains at Dolores, Colo. (Photo by U. S. Geological Survey.) 

rain. On a larger scale they are formed where the small streams 
from the river bluffs meet the flood plain of the river. On a 
much larger scale they are formed where the streams from high 
mountains, like the Sierras or the Rockies, first meet the border- 
ing plain. 

The alluvial fan of King's River extends entirely across the 
San Joaquin Valley, forming the Tulare Basin. The alluvial 



290 



ELEMENTS OF PHYSICAL GEOGRAPHY 



fans formed by the different streams flowing from the San 
Bernardino Mountains of southern California overlap, forming 
a continuous piedmont alluvial fan at the base of the mountains. 




Fig. 193. — Alluvial fan of King's River, which extending across the San Joaquin 
Valley has obstructed the drainage, forming the Tulare Lake basin. 

This is part of the great fruit district of southern California, 
extending from Redlands to near Los Angeles (Fig. 193). 

279. Alluvial Cones. — Cone-shaped deposits are formed at 
the base of steep mountains, where some of the material is carried 
down by gravity. They grade through talus cones, where much of 



RIVERS 



291 



the material is carried by gravity, to the talus slopes, where most of 
it is accumulated by gravity. In fact, many talus slopes are made 
up in part of alluvial cones and fans (Fig. 194). 

280. Deposits on Flood Plains. — In flood season the channel 
of a river is not large enough to carry all the water. The 
excess spreads out over the broad flats or flood plains bordering 
the channel. As the flood begins to subside the volume of 
water is decreased, the velocity is checked and the sediment 




Fig. 194. — Alluvial cone at base of mountain. Formed of rock fragments 
loosened by weathering and carried down the slope by gravity and rain wash. 

carried by the flood plain waters is deposited over the flood 
plain, adding another layer to the rich deposit of former floods. 
Since this deposit consists of the finest and richest portions 
of the soils from the hillsides of the upper valley, flood plains 
have proverbially rich soils and hence are productive farming 
regions. 

281. Natural Levees. — Levees are formed naturally on 
the immediate banks of the streams bordered by flood plains. 
Where the swifter waters of the overflowing channel first meet 
the slower-moving flood-plain waters, there is the greatest check 



292 



ELEMENTS OF PHYSICAL GEOGRAPHY 



in velocity and hence the greatest deposition, which builds up 
a ridge or natural levee. The upbuilding of the natural levee 
is aided by the growth of bushes and trees, which in time of 

overflow act in further 
checking the velocity 
and thus increasing 
the deposit 

The levees interfere 
with the tributaries 
flowing into the main 
stream. On the flood 
plain of the lower 
Mississippi (see Fig. 
195) many of the tribu- 
taries flow along the 
flood plain more or less 
parallel with the main 
river for many miles 
before they find an 
opening through the 
levee. Many small 
tributaries flow from 
the levee directly away 
from the river. (See 
Donaldson Sheet of 
the United States 
Topographic Atlas.) 

282. Artificial Lev- 
ees. — Man attempts 
to improve on nature's 
methods by adding material to the top of the natural levees, 
producing artificial ones in the endeavor to keep the river 
in its channel and prevent it from overflowing the flood 
plain. As the levee is built up, the river deposits material on 




Fig. 195. — The lower Mississippi River below 
Cairo. The black lines along the river are levees. 



RIVERS 293 

the bottom of the channel, making it necessary to keep adding 
to the top of the levee, until it is sometimes built up many feet 
above the bordering area, so that steamboats in the river are 
sometimes above the level of the neighboring farms. A break 
in such a levee (called a crevasse) often proves to be very de- 
structive on the bordering flood plain. Sometimes the river 




Fig. 196. — Levee on the Yuba River, Calif. Protected flood plain at right, 
river at the left. (Photo by U. S. Geological Survey.) 

even leaves the existing channel permanently and forms a new 
channel elsewhere to repeat the process, and in this way by a 
repetition of such changes finally raises the level of the whole 
plain (Fig. 196). 

283. Deltas. — A river flowing into a body of still water, as 
a lake or the ocean, where there are no strong tides, deposits 
all of its load of sediments, building up an accumulation called 
a delta. There is generally no sharp line of separation between 
the delta and the flood plain ; the latter has been built up on 



294 



ELEMENTS OF PHYSICAL GEOGRAPHY 




the land and the former has been formed in the sea or lake. 
The river divides on the delta and finds its way into the sea 
by several, sometimes by a great many channels, called distribu- 
taries. The head of the delta is frequently located where the first 
distributary leaves the main channel. Deltas, like flood plains, 
have a fertile soil and frequently support a dense population. 
Both delta and flood plain are fertile because they are com- 
posed of the rich surface soil from other parts of the basin. 
The soil contains much humus and is frequently renewed. 

284. Structure of a Delta. — As shown by the accompanying 
diagram, the structure of a delta is characteristic. The middle por- 
tion consists of mingled sand and mud beds formed at the end of 

the delta, where the 

A 



river current first 
meets the still water. 
At this point a larger 
part of the load is 
dropped than at any 
other, and the mate- 
rial comes to rest in 
inclined layers, the fore-set beds, dipping towards the open water. But 
some of the fine materials is carried out into deeper water, forming 
the mud layers that sometimes reach considerable thickness and great 
extent, the bottom-set beds, which form the submarine delta (Fig. 197). 

The delta of the Indus River has built up the submarine portion 
nearly to the sea level over such an extensive area of now shallow 
sea that in places large vessels cannot get within sight of the shore. 

Over the top of the fore-set beds is a deposit of horizontal beds, 
the top-set beds, made by the river in flood time and not essentially 
different from the flood plain deposits ; in fact, it is the extension of 
the upper flood plain over the top of the underlying delta material. 
All these structural features may be observed in the mud deposit formed 
in a pool on the roadside by a summer shower. By recognizing such 
delta structure in the bed rocks of the continent the geologist deter- 
mines the location of deltas in past ages. 

285. Work of Rivers. — The work of the rivers consists in 
dissecting the upland areas and carrying the material along 



Fig. 197. — Delta structure. A, top-set beds ; B, 
fore-set beds; C, bottom-set beds; S, sea level. 



RIVERS 295 

with the excess rainfall to the lowlands and finally to the sea. 
In this work it is assisted by the weathering agents, such as 
wind, frost, heat of the sun, gravity, chemical action, and animal 
and plant life, which cause the rocks to disintegrate and crumble 
into fragments. The rain washes the loose materials into the 
stream channels, and the current carries them toward the sea. 
The journey is not a continuous one because the material is 
dropped and picked up again many times between the mountain 
and the sea. Thus, when a river flows into a pond or lake, 
nearly all the sediment is deposited until the lake or pond is 
completely filled, after which the river, under new conditions, 
picks up the materials and carries them to a lower level. (See 
Figs. 245 and 246.) 

So with the alluvial fan and flood-plain materials, which are 
deposited by the rivers in grading their courses. In time, with 
change of grade in the channel, these materials are again moved 
toward the sea. 

The first effect of the river work is to diversify and roughen 
the topography by dissecting the higher plains, plateaus, and 
mountain masses into hills and valleys. The work goes on 
most rapidly when there is the maximum number of steep 
hillsides. Hence, the work goes on slowly while the valleys 
are first forming. It then increases rapidly until the upland 
is completely dissected. The intensity of the work then 
decreases as the hills are lowered and the slopes on the hill- 
sides become less and less steep, until all the uplands are worn 
down to the level of the low plains. 

286. Life History of a River — The Cycle of Erosion. — The 
successive changes which a stream undergoes from the time it 
starts on an upland area until the upland has been reduced to 
a lowland, constitutes the life history of the stream. It has 
a beginning, a period of development, decline and disappearance. 
It is customary to distinguish at least three different stages in 
the cycle, as youth, maturity, and old age. 



296 ELEMENTS OF PHYSICAL GEOGRAPHY 

287. Youth. — Youth is the period of rapid growth in the 
beginning of the cycle. Some, of the characteristics of this are 
narrow, V-shaped valleys, cataracts and rapids, lakes and 
swamps on the upland and inter-stream areas, few tributaries, 
and broad stretches of undrained or poorly drained country 
bordering the valley. The conditions, of course, are different 




Fig. 198. — Valley in youthful stage of erosion in soft rocks on the coastal 
plain, Maryland. (Photo by Maryland Geological Survey.) 

on a stream developing on a plain from one on the plateau or 
mountain, yet the youthful stage of each can be recognized 
from its advanced or mature stage by some or all of the above 
features. Fox River on the Ottawa, Illinois, topographic 
atlas sheet and Red River on the Fargo sheet are types of 
topographic youth. (See Figs. 198 and 199.) 

288. Maturity. — Maturity of streams is characterized by 
the absence of lakes and swamps, which have been filled or 



RIVERS 



297 



drained, the absence of cataracts, decrease in the number of 
rapids, increase in the number of tributaries, and complete 
dissection of the inter-stream areas. The divides are sharp 
ridges. There is some shifting of the divides. The sides of 
the valley are steep, with many cliffs and talus slopes ; small 
flood plains have developed in places, the river is beginning to 
meander ; the cross sections of the valley are changing from a V- 




Fig. 199. — Valley in youth in very hard rock (quartzite), Ausable Chasm, 
N. Y. (Photo by H. M. Brock.) 



shape to a U-shape. In the mature stage the erosion is at the 
maximum, and there is the greatest percentage of steep hillsides 
over the area. A large per cent of the rainfall is conducted 
rapidly into the stream channels, resulting in destructive 
floods in the wet season. The tributaries of the Ohio River 
in West Virginia are good examples. In the mature stage the 
upland plains have almost or entirely disappeared, that is, 
they -have been dissected by the stream and its tributaries 



298 ELEMENTS OF PHYSICAL GEOGRAPHY 

into hills and valleys, the tops of the hills being the remnants 
of the former upland plains or plateaus (Fig. 200). 

289. Old Age. — In old age the narrow sharp divides of the 
mature stage are cut down into low rounding hills with gentle 
slopes; the cliffs have disappeared; flood plains increase in 
size with corresponding increase in the meanders of the river, 




Fig. 200. — Valley in maturity. Cheat River in the Allegheny Plateau, W. Va. 
(Photo by U. S. Geological Survey.) 



and formation of oxbow lakes. Deltas increase in size and 
natural levees and river swamps become prominent. (Study 
the diagrams showing changes in profile and in cross section, 
also the contour maps cited, and the streams seen in your field 
trips.) In extreme old age the hills and uplands are nearly all 
worn down to the level of the valley, when the whole area is 
called a peneplain, the final stage of erosion being that of base 



RIVERS 299 

level (Sec. 257). The most resistant rocks that remain as 
hills on the worn-down area are called monadnocks (Fig. 201). 
(See also Figs. 285 and 286.) In old age the upland plains 
have disappeared and lowland plains have formed and are 
increasing in size. Lakes and swamps are forming on the 
flood plains, but have all disappeared from the upland (Fig. 201). 




Fig. 201. — Old age stage of erosion. A monadnock (Mt. Pony) on pene- 
plain, near Culpeper, Va. (Photo by Maryland Geological Survey.) 



290. Accidents or Interruptions to the Cycle. — The cycle 
of erosion on a hard rock area is so long that there is generally 
an interruption of some sort before any river completes the 
whole cycle. The principal interruptions to the cycle are eleva- 
tions or depressions of the whole or a part of the area drained 
by the river. There is abundant evidence that many land 
areas have been elevated and depressed several times during 
their history. In a great many places at the present time the 
land is slowly rising and in other places sinking. (See Chapter 
XL) 



300 ELEMENTS OF PHYSICAL GEOGRAPHY 

The depression of the lower portion of a river basin carries 
part of it below the level of the sea, which extends up the valley 
as a bay, such as Delaware or Chesapeake Bay, or an estuary, 
such as the Hudson River below Troy. The river is dismem- 
bered of its tributaries on the drowned portion. Thus the 
Potomac, Rappahannock, York, and James rivers that now 
flow into Chesapeake Bay were tributaries of the Susquehanna 
River before it was drowned. (Study contour sheets for 
examples of dismembered rivers.) 

If the middle or upper portion of a river valley is depressed 
more than the lower portion, a swamp or lake will be formed 
in the sunken part. Reelsfoot Lake in west Tennessee occupies 
a sunken portion of part of the Mississippi flood plain that sank 

during the earthquake in 
1811. 

291. Revived Rivers. — 

When a river basin is ele- 

Fig. 202. — doss sections of valleys vated in such a way as to 

in youth , AA; maturity B and C ; and i ncrease the velocity of the 
old age, D ; M is a monadnock. ... 

stream, it begins to degrade 
and further lower its channel. It is then said to be a revived, 
rejuvenated, or entrenched river. If such an elevation takes place 
while the stream is still in youth, it is difficult to detect. But 
if it should be revived when it is in maturity or old age, then 
the new valley entrenched in the bottom of the old shows 
youthful features in marked contrast to the upper or older part 
of the valley. 

292. River Terraces. — After the revived stream has 
widened the entrenched part of its valley, the remnants of the 
flood plain of the old valley form alluvial terraces on the slopes 
of the deeper valley. Terraces at two different levels signify 
that the stream has been revived twice. Three well-marked 
terrace levels along the Shoshone River at Cody, Wyoming, 
indicate at least three separate uplifts of that region (Fig. 203). 



B 

• -e 
D- 



RIVERS 301 

Alluvial terraces bordering river valleys are also formed by 
the filling of lakes or dams in the river valley, and the entrench- 
ing of the river in such a deposit. These can generally be 
distinguished from the common terraces of remnants of river 
flood plains, by their more abrupt termination at the down- 
stream end of the terrace. 




Fig. 203. — River terraces along the Shoshone River at Cody, Wyo. (Photo 

by the author.) 

In a glaciated region, such as the northern United States, there are 
many sand and gravel terraces on the hillsides formed by accumu- 
lations on the margins of ice lobes during the waning period of the 
glacier, and in temporary glacial lakes formed by the glacier in the 
river valleys. 

Alluvial terraces should not be confused with rock terraces, which 



302 



ELEMENTS OF PHYSICAL GEOGRAPHY 




form on the hard strata where a stream cuts its valley through hori- 
zontal beds of hard and soft rock. (See Figs. 203, 204, and 205.) 

293. Reversed Drainage. — If the lower or middle portion of a river 
basin is elevated more than the upper portion and the elevation proceeds 

faster than the downcut- 
ting of the stream, the 
waters of the upper basin 
may be spilled over the di- 
vide and the drainage of 
the upper basin reversed. 
Such a reverse causes a 
shifting of the divide. 

294. Stream Piracy, Water Gaps, Wind Gaps. — During 
the youth and maturity of streams developing on a land area, 
some of the streams enlarge their valleys faster than others, 
frequently at the expense of others. This is notably the case 



Fig. 204. — Alluvial terraces, tt, t't' , formed 
by two periods of rejuvenation of a river. F, 
present flood plain. 




Fig. 205. — Coal terraces in Allegheny Plateau, formed at the outcrop of 
coal seams on hillside. Rock Terraces. 



where streams flow across the edges of alternating hard and 
soft layers, as indicated in Figs. 206 and 207. 

All of the streams in Fig. 206 are checked in the rate of down- 
cutting by the hardness of layer A. If one of the streams, as 
No. 1, finds a softer place in A or receives more water, it cuts 
down faster than any of the others. The advantage once 



RIVERS 



303 



gained is rapidly increased, just as a rich man accumulates 
wealth faster than a poor man, because additional wealth in 
one case, additional volume of water in the other, gives ad- 
ditional power. 

As stream No. 1 erodes its channel through A faster than the 
other streams, so its tributaries a and b lower their channels 
faster than the others, until finally they extend successively 
into the basins of 
2, 3, and 4, grow- 
ing more rapidly 
with each addi- 
tional stream cap- 
tured. Stream No. 
1 is the pirate 
stream; the others 
are beheaded. 

The more rapid 
erosion of the softer 
layers in Fig. 206 
leaves the harder 
layers A and B 
standing up as 
mountain ridges or 
hiUs in Fig. 207. 
Stream No 1 has 
cut deep notches 
in the ridges at 

WW, which are called water gaps. The smaller streams 2, 3, 4, 
and 5 cut depressions in these hard layers before they were 
beheaded, which are called wind gaps. 

Consult the map of Pennsylvania and see how the Penn- 
sylvania Railroad takes advantage of the water gaps in getting 
through the ridges of the Allegheny Mountains. Do other 
railways and highways pass through the gaps? Why? Most 




Fig. 206. — An early stage in river piracy. AA 
and BB, outcropping edges of hard rocks across which 
the streams flow. See Fig. 207. 



304 



ELEMENTS OF PHYSICAL GEOGRAPHY 



wind gaps are evidence of former stream piracy and the shifting 
of divides. 

295. Examples of River Piracy. — A typical example of 
river piracy is the Shenandoah River, as shown in Fig. 208. 
This is only one of scores of similar instances in the Allegheny 

Mountains where 
the final result has 
been the develop- 
ment of the so- 
called trellised 
drainage, in which 
the tributaries join 
the larger stream at 
right angles like the 
branches of a vine 
on a trellis. 

Good examples of 
recent stream piracy 
are shown on the 
Kaaterskill topo- 

graphic sheet in the 
Catskill Mountains 
of New York. The 
creeks flowing down 
the steep eastern 
slope into the Hudson 
are cutting down fas- 
ter than those flowing 
west or southwest on 
the gentle slope into the Susquehanna. Because the east-flowing Hud- 
son tributaries cut down faster they also lengthen their valleys faster. 
When the head of one of these lengthening valleys meets one of the 
Susquehanna tributaries, the water is all diverted into the Hudson 
tributary, and the Susquehanna tributary is beheaded. 

296. Consequent Streams. — Consequent rivers are those 
which follow the general slope of the land and take the most 




Fig. 207. — A later stage than that shown in Fig. 
206. Stream No. 1 has gained more water and 
deepened its channel faster than 2, 3, 4, and 5. 
Hence, its tributaries have captured the upper por- 
tions of the other streams, leaving wind gaps at 
PPP, and forming water gaps at WW. Stream 
No. 1 is the pirate stream. 



RIVERS 



305 



direct course from the uplands to the lowlands. All gullies 
and nearly all streams in their early stages as they develop 
on new land areas are consequent streams (Fig. 209) . 

297. Subsequent Streams. — As streams deepen their val- 
leys, if they cut into layers of rocks of different degrees of hard- 
ness and inclined to the horizontal, the erosion on the softer 




Fig. 208. — River piracy on the Shenandoah River, Va. Drawing after 
Willis. The Potomac River has deepened its channel through the Blue Ridge 
faster than Beaverdam Creek, hence the Shenandoan tributary has lowered its 
channel below that of Beaverdam Creek west of Blue Ridge and captured the 
headwaters of the latter creek. 



rocks will go on more rapidly than on the hard layers, and many 
streams that were originally consequent streams are shifted 
to the softer layers. In this shifting of streams to the softer 
rocks, the streams adjust themselves to the rock structure. 
This readjustment of streams to the structure goes on during 
late youth and maturity, and such streams are called subsequent 



306 



ELEMENTS OF PHYSICAL GEOGRAPHY 



streams. They are in part the result of river piracy. (See 
Figs. 207 and 208.) 

298. Antecedent Streams. — Antecedent streams are streams 
flowing through mountains, plateaus, or highlands which have been 
elevated across the course of the stream so slowly that the streams 
cut down their channels as fast as the elevation took place. Such 
streams are called antecedent, because they were there first. The 




Fig. 209. — Consequent stream courses, near Colfax, Calif. 
Geological Survey.) 



(Photo by U. S. 



Susquehanna and Potomac Rivers are antecedent to the Allegheny 
Mountains through which they flow. They are also superimposed 
rivers. The Columbia River is antecedent to the Cascade Mountains 
(Fig. 210). 

299. Superimposed Streams. — All streams flowing on loose 
rock material on comparatively level plains of any kind, such as 
glacial, coastal, lacustrine, or alluvial plains, develop a meandering 
course. When such a plain is elevated the stream is revived and 
entrenched in its old channel. (See Sec. 291.) 

If the deepening continues, the stream finally cuts through the 



RIVERS 



307 



alluvial soil or soft mantle rock into the hard bed rock underneath, 
still keeping its meandering course. In time the alluvial material 
of the original plain is carried away by erosion and the stream has 
its former winding course in hard rock. It has been superimposed 
on the hard rocks with a winding channel developed on formerly 
overlying soft material. See the Kanawha River in West Virginia, 




Fig. 210. — View on Columbia River where it cuts through the Cascade 
Mountains. The river is antecedent to the mountains. (Photo by Weister.) 



and the Canodoguinet River in Pennsylvania, on the Harrisburg 
topographic sheet. All rivers flowing in meandering valleys in hard 
rocks are superimposed rivers. 

300. Streams in Arid Climates. — There are some forms of 
erosive action that are characteristic of dry and arid climates. 
In desert regions the little rain that falls descends in heavy 
thunder showers, separated often by long intervals, some- 
times several months, sometimes several years. The long 
intervals of dry weather cause the death of all vegetation, 



308 ELEMENTS OF PHYSICAL GEOGRAPHY 

and the heavy rains, falling on the bare soil, flow rapidly into 
and along the channel ways, called wadies in the Sahara, there 
cutting deep trenches with steep, frequently perpendicular 
sides. The wady is frequently used as a highway by the 
traveler on the desert, because he there finds some shade and 
protection from the hot scorching winds of the desert, and 




Fig. 211. — An arroyo near Kingman, Ariz. A stream course in an arid 
region. (Photo by D. T. McDougal.) 

furthermore any water hole in the region is likely to be there. 
It is because these wadies are so frequented by travelers 
that sometimes persons are drowned in them by the down- 
rushing flood following one of the sudden storms. Similar 
deep gullies cut by the heavy rainfalls in the arid regions of 
the southwest United States are called arroyos, washes, draws, 
or canyons. (See Fig. 211.) 

There are many " lost rivers " in an arid region. The heavy 



RIVERS 309 

rainfall on the mountain cuts deep gullies and ravines on the 
steep slopes, but when the stream flowing in such a gully 
reaches the plain at the base of the mountain, it spreads out 
over the alluvial or colluvial material, where much of it is 
evaporated and the remainder sinks underground and is lost 




Fig. 212. — Erosion in a semiarid region. Big Bad Lands, S. Dak. (Photo 
by U. S. Geological Survey.) 



as a surface stream. Lost rivers also occur in humid regions 
where the stream flows into a sink hole in a limestone area 
and becomes a subterranean or cave stream. 

301. Playas. — In interior basins, that is, areas in which the 
rivers have no outlet to the sea, there are broad shallow depressions, 
probably formed by the wind, that are covered with water after a 
heavy rain, but from which the water is evaporated during the long 
dry seasons. Such areas are called playas, a Spanish word meaning 
shore or strand. A playa of this kind occurs in Black Rock Desert 
in Nevada, covering nearly a thousand square miles, which in the wet 
season is covered with water a few inches deep, carried in by the Quinn 
River, which flows into it. When the water is agitated by high winds, 



310 ELEMENTS OF PHYSICAL GEOGRAPHY 

it becomes a lake of mud. During the summer season the water 
evaporates and leaves the area a barren clay flat. Deeper depressions 
may form salt lakes. 

302. Bad Lands. — The so-called bad lands of the west and 
middle west are striking examples of a type of stream work 
most marked in semiarid regions. They are areas having an 




Fig. 213. — Erosion in a semiarid region, Bates Hole, Wyp. 

excessive number of deep gullies separated by steep hills carved 
into varied and fantastic forms. Such areas were named 
bad lands because they were so difficult to cross, and so useless 
for agriculture. The name is sometimes applied to much 
gullied hill slopes in the eastern states, but all such are but 
faint imitations of the big bad lands of the west. 

The largest bad-land areas are in northern Nebraska and 
southwest South Dakota, south and east of the Black Hills. 



RIVERS 311 

They were utilized as hiding places by the Indians in the Indian 
wars. It was almost impossible for an army to discover a 
band of Indians in such a complex maze of hills and gullies 
(Fig. 212). 

Many of the smaller bad-land areas in the west are called 
holes, such as Bates Hole, some miles south of Casper, Wyo- 
ming, and the Devils Kitchen, some fifty miles west of Casper 
(Fig. 213). 

QUESTIONS 

1. Do gullies form more rapidly in fields or in forests? Why? 

2. Define river channel, river valley, river basin. Which under- 
goes most rapid changes? 

3. Why are stream channels deepening more rapidly in some places 
than in others ? How does local deepening cause rapids or falls ? 

4. Base level is differently defined by various writers. Write your 
definition and explain. 

5. Why do valleys in a humid climate widen more rapidly than 
those in an arid climate ? 

6. Why more rapidly in maturity than in youth? 

7. Why is the valley of the Mohawk River much wider than that 
of the Niagara River? 

8. Most streams, even small brooks, have flood plains. Why is 
there no flood plain along the Niagara River? 

9. Make a drawing of any oxbow cut-offs on near-by streams. 

10. What would be the corrading power of a stream after the 
velocity increased 4 times ? 40 times ? 400 times ? 

11. What would be the transporting power after velocity increase 
of 4? 40? and 400? 

12. Would your results for Nos. 10 and 11 be true if the stream was 
loaded with sediment both before and after the increase? Would 
they be true if the water carried no sediment? 

13. Make a list of all the waterfalls you have seen, and state to 
which type each one belongs. 

14. If the layer of hard rock at the top of Niagara Falls were much 
thinner than it is, what effect would it have on the falls? If it were 
much thicker? If it formed the entire cliff and there were no soft rock? 

15. Why are there so many waterfalls in New England and New 
York? • • 



312 ELEMENTS OF PHYSICAL GEOGRAPHY 

16. Explain the advantage gained by building dams or artificial 
lakes on the tributaries of the Ohio and Mississippi rivers. Do you 
think the saving would justify the expense? What effect do you 
think such construction would have on the lower Mississippi River? 

17. Suppose the continents were all base leveled. What would 
be the effect on the climate ? On animal life ? 

18. Describe a small delta formed during a heavy rain. With a 
shovel remove longitudinal and transverse sections to show attitude 
of the layers. 

19. Write out in your own words the life history of a river as you 
understand it, citing some examples illustrating each stage. 

20. Examine alluvial terraces in your vicinity. Are they of river 
flood plain, lacustrine, or glacial origin? State your reasons. 

21. Describe some examples of river piracy on the Kaaterskill, 
New York, contour map. Make sketches showing position of divide 
before and after piracy. 

22. Explain lost rivers in desert areas. How do they differ from 
lost rivers in the Allegheny Mountain region? 

23. Describe bad-land topography. Why is it more common in 
semiarid than in humid regions? 



CHAPTER IX 

GLACIERS 

A glacier is a mass of moving ice that has been formed in a 
region of perpetual snow. It is an active agent of erosion and 
transportation of rock material, and in regions in which glaciers 
occur they are among the most important agents in carving the 
rocks into the varied landscape features. The grandest scenery 
in the world is associated with the presence and the work of 
glaciers. Switzerland with its many glaciers is so famed for its 
picturesque scenery that to call any portion of our country " the 
Switzerland of America " is considered the highest compliment 
we can pay to its beauty. 

303. Origin of Glaciers. — Glaciers originate in snow fields, 
which are regions that remain covered with snow from year to 
year. In most regions the snow that falls during the winter 
season melts during the warm season. In some regions the 
cold season is so long and the warm season so short that not 
all the winter snow is melted and the residue accumulates from 
year to year. The snow gradually changes into a granular 
mass composed of little pellets of ice, known as neve, which 
resembles coarse salt in appearance. The neve merges down- 
ward into hard blue ice, which forms the base of the snow field 
and the source of the glacier. The streams or sheets of ice 
moving out from snow fields are called glaciers (Fig. 214). 

304. Occurrence of Glaciers. — The long cold season nec- 
essary to form snow fields and glaciers occurs at high altitudes 
or high latitudes. Within the tropics they occur only on the 

313 



314 



ELEMENTS OF PHYSICAL GEOGRAPHY 



highest mountains at elevations of three miles or more above 
sea level. Towards the poles they occur at successively lower 
levels, down to sea level in places near the poles. 

Small snow fields occur on the high peaks of the Rocky Moun- 
tains in northern Colorado, in Wyoming and Montana, and on 
the high peaks of the Pacific Mountains in California, Oregon, 




Fig. 214. — Gorner Glacier, tributaries, moraines, and snow fields. View at 
Gorner Grat, Switzerland. (Photo by H. L. Fairchild.) 

and Washington. Larger ones occur on the mountains farther 
north in Canada and Alaska. Nearly all of Greenland is covered 
with a vast snow field thousands of square miles in extent. The 
largest snow field in existence at the present time is on Ant- 
arctica, the region about the South Pole. 

Small snow fields and glaciers occur on the high mountains in 
Mexico and Central and South America, with larger ones toward the 
south end of South America. They occur in the Alps, Himalayas, 
and all the great mountains of the world. 



GLACIERS 315 

305. Types of Glaciers. — (1) The very large glaciers, like 
those of Greenland and Antarctica, are called continental glaciers. 
(2) The smaller ones that form on mountains and flow down 
the valleys are called mountain glaciers or valley glaciers, or 
more commonly alpine glaciers because of their abundance in 
the Alps Mountains. (3) Cliff glaciers or glacierets are small 




Fig. 215. — A cliff glacier. Rainbow Glacier in Glacier National Park. 
(Photo by U. S. Geological Survey.) 

alpine glaciers that occur in the depressions on steep mountain 
sides and do not extend much beyond the edge of the snow 
field which forms them (Fig. 215). (4) Piedmont glaciers are 
formed by two- or more alpine glaciers that spread out and 
unite at the base of the mountains. The Malaspina Glacier 
in Alaska is an example of a piedmont glacier. 

306. Alpine Glaciers. — The alpine glacier begins to melt 
as soon as it leaves the snow field, and the distance which the 



316 



ELEMENTS OF PHYSICAL GEOGRAPHY 



ice moves down the valley before it is melted depends largely 
on the size of the glacier, the steepness of the slope, and the 
warmth of the atmosphere. Some of the cliff glaciers are all 
melted within a few hundred feet of the snow field. The 
Aletsch glacier in Switzerland extends down the valley fifteen 




Fig. 216. — Mt. Rockwell and Two Medicine Lake in Glacier National Park. 
U-shaped glacial valley on each side of Mt. Rockwell. (Photo copyrighted by 
R. E. Marble.) 



miles before it is melted. The lower end of a glacier marks 
the place where the amount of ice melted is equal to the amount 
moved forward. An increase in the forward movement or a 
decrease in melting means a lengthening of the glacier and vice 
versa. 

307. Erosion by Alpine Glaciers. — As the stream of ice 
of an alpine glacier moves down the valley from the snow field, 



GLACIERS 



317 



it wears away the rock over which it moves, by means of the 
rock material carried in the bottom of the ice. Since many 
of the alpine glaciers are quite deep, they wear the sides as 
well as the bottom of the valley. The result of this erosion 
by the glaciers is to deepen and widen the valley, changing the 
V-shaped valley to a U-shape. It differs from the U-shaped 





w 




^j^^g^Rar iJ 


\*~- ^&^- . 





Fig. 217. — Glacial grooves in U-shaped glacial valley, in the San Juan 
Mountains, Colo. See also Fig. 226. (Photo by the author.) 

river valley in having a grooved, smoothed, and polished bed- 
rock floor, covered in places by moraine material, instead of an 
alluvial floor (Figs. 216 and 217). 

Erosion goes on at the bottom and sides of the snow basin which 
holds the snow field. In warm weather the ice expands and is thrust 
against the rock walls. In cold weather the ice in the snow field 
contracts and pulls away from the sides of the basin in which it occurs, 
forming a huge crevasse or crack called a bergschrund. Boulders and 
masses of rock are plucked from the rock walls of the basin, others 



318 



ELEMENTS OF PHYSICAL GEOGRAPHY 



fall into the bergschrund to be frozen into the ice and carried away, 
thus enlarging the basin. This process, repeated year after year, 
widens and deepens the basin into a great amphitheater, known as a 
cirque. Where a number of cirques or snow basins occur on different 
sides of the same mountain mass this cutting back at the bottom and 
sides forms steep, rugged rock cliffs above the level of the snow field, 
giving a grandeur to the mountain scenery unsurpassed by any other 




Fig. 218. — Glacial cirques in San Juan Mountains, Colo. Continental 
divide in the background. (Photo by the author.) 

form of erosion. Erosion of this kind may be seen in all mountains 
where glaciers occur. Many fine examples may be seen in Glacier 
National Park, through the Rocky Mountains from southern Colorado 
into northern Canada, and in the Alps of Switzerland (Figs. 218 and 222). 

308. Transporting Work of the Alpine Glaciers. — Alpine 
glaciers transport vast quantities of rock material ; some in 
the bottom of the ice, called subglacial or ground moraine, some 
in the midst of the ice, called englacial, and some on the surface, 
called superglacial. 



GLACIERS 319 

As a, glacier moves down the valley, rock material falls from 
the cliffs and mountain sides on to the margin of the glacier 
and is carried along by the ice as it moves. This is called the 
lateral moraine because it is formed at the sides of the glacier. 
If there were no glaciers in the valley, this rock material would 
form a talus slope. Hence the lateral moraine is the talus 
slope material moved along by the ice. 



H^fete 


> 


sf-.-.-': ; .• . ■ ■ 









Fig. 219. — Aletsch Glacier, Switzerland, showing medial moraine. See 

also Fig. 214. 

When two tributary glaciers unite, the lateral moraine of 
each tributary on the sides where they unite is carried down 
the middle of the glacier below the junction. It is then called 
medial or middle moraine. A glacier that has many tributaries 
has many lines of medial moraine. Lateral moraine and the 
medial moraine are subdivisions of superglacial moraine 
(Fig. 219). 



320 ELEMENTS OF PHYSICAL GEOGRAPHY 

The rock material carried along in the bottom of the ice is 
called the ground moraine. The accumulation at the lower end 
of the glacier, composed of the material of the lateral, medial, 
and ground moraines, along with the englacial material, forms 
the terminal moraine (Fig. 220) . 




Fig. 220. — Terminal moraine of an alpine glacier. Three Sisters Glacier, 
Ore. (Photo by U. S. Geological Survey.) 



If the glacier moves forward after building a terminal moraine, it 
pushes part of the terminal moraine in front of it. This is called a 
push moraine (Fig. 221). 

309. Advance and Retreat of Alpine Glaciers. — The lower 
end of an alpine glacier is not always at the same place. In 
general all the alpine glaciers are smaller than they formerly 
were, as shown by the evidence of the erosion and the moraines 
left in the valleys, in some instances many miles down the valley 



GLACIERS 



321 



from the present terminus. Moreover in many places in the 
southern Rocky Mountains and in the southern Sierra Nevada 
Mountains in California and in other mountains, there is evi- 
dence of the existence of alpine glaciers in the past, although 
there are no glaciers at present. 

Observations on glaciers in the Alps for a century or more 
have shown that while in general the glaciers are becoming 
smaller, there have been periods when for some years they in- 




Fig. 221. — Push moraine. La Perouse Glacier, Alaska. (Photo by U. S. 
Geological Survey.) 



creased in size and the termini pushed farther down the valleys. 
In some places in the Alps the land is cultivated up to the end 
of the glacier and during a period of advance the ice moves 
down into the fields, destroying fences and other farm 
property. 

The advance of the end of glaciers is caused by heavier snow falls 
in the mountains accompanied by longer winters and hence a decrease in 
the amount of melting ; that is, there are periods of floods in glaciers 
just as in rivers, the difference being that the river flood follows directly 
after the exceptionally heavy rainfalls or the rapid melting of un- 
usually heavy snows. The rate of movement of a glacier is so slow 



322 ELEMENTS OF PHYSICAL GEOGRAPHY 

that the effects of the flood are separated from the cause by years, 
instead of hours as in the case of rivers. 

310. Effects of Advance and Recession. — One effect of the ad- 
vance and recession of the glacier is a change in the terminal moraine. 
During the forward movement the glacier moves over the terminal 
moraine of preceding years, generaUy pushing or carrying a large part 
of it along and distributing it farther down the valley. During a reces- 
sion of the ice the end of the glacier moves up the valley, leaving the 
terminal moraine as a hill or ridge of fragmental rock across the valley. 

While the recession continues, however slow it may be, the moraine 
is distributed more or less uniformly over the valley floor below the 
end of the retreating glacier. When the end of a glacier is stationary 
or nearly so for a number of years, that is, when the rate of melting 
at the lower end of the glacier is just equal to the rate of movement, 
the terminal moraine accumulates and forms a ridge or dam across the 
valley, a terminal moraine of recession. A further recession of the ice 
causes the water from the melting glacier to accumulate behind the 
moraine, forming a lake. Many of the beautiful mountain lakes are 
formed in this way. 

As one stands on Arapahoe Peak in Colorado and looks down on the 
glacier, he can see such a lake in the process of formation at the end 
of the ice behind the moraine, and looking farther down the valley, 
he can see a dozen or more similar lakes scattered at intervals as far 
as the eye can reach. A great many of the charming lakes in Glacier 
National Park and elsewhere were formed in a similar manner. 

311. Cirque Lakes. — When an alpine glacier is all melted 
there is nearly always a lake left in the cirque or snow basin. 
The smaller cirque lakes are soon filled up with talus from the 
bordering rock cliffs, but many alpine glaciers have so re- 
cently disappeared from the Rocky Mountains that scores of 
cirque lakes still remain. See the Telluride and Silverton, 
Colorado, topographic sheets and the topographic map of 
Glacier National Park (Fig. 222). 

312. Alpine Glaciers Compared with Rivers. — In some 
ways glaciers are like rivers ; in others very much unlike them. 
Alpine or valley glaciers resemble rivers in flowing through 
valleys or elongated depressions in the surface and along the 



PLATE IV 







Grinnell Mt 




<jjj V GrinrielL 
*L Glacier* 

^X__ Gould Mt. 



Part of Chief Mountain, Mont., Sheet, U. S. Geological Survey. 

Part of Glacier National Park, Showing Glaciers, Cirques, 
Cirque Lakes, and Morainal Lakes in the Valleys. The Broken 
Black Line is the Continental Divide. The Solid Brown Color 
Marks Vertical or Nearly Vertical Cliffs. 



GLACIERS 323 

lowest part of the valley ; in having crooks and turns, and falls 
and rapids ; in moving faster at the top than at the bottom, 
faster on the outside of a curve than on the inside ; in moving 
more rapidly and having a rougher surface on the steeper 
portions of the channel, namely the falls and rapids, than on 
the level portions ; in being fed by moisture precipitated from 




Fig. 222. — Glacial cirque lake and hanging valleys. Avalanche Basin, 
Glacier National Park. CPhoto copyrighted by R. E. Marble.) 

the atmosphere ; in carrying this precipitated moisture to or 
towards the sea level ; and in carrying vast quantities of rock 
material from higher to lower levels. 

Glaciers differ from rivers in moving much more slowly — 
inches per day instead of miles. Both are fed by rains and 
snow, but rivers are fed chiefly by rain and groundwater, while 
glaciers are fed almost entirely by snow. The source of a 
glacier is always a snow field ; of a river it is springs, seepage, 



324 ELEMENTS OF PHYSICAL GEOGRAPHY 

lakes, or a glacier. Glaciers carry more and coarser material 
on the surface than a river, which carries all its coarse ma- 
terial by rolling and pushing it along the bottom. 

Rivers may carry heavy loads down steep slopes, but they drop the 
greater part of the load on the first flat, while glaciers carry heavy 
burdens over flats and in many cases even up a hill. The river carries 
most of its burden during the flood season, dropping much of it with 
the subsidence of the flood, while the glacier carries its burden steadily 
along until it drops it at the end of the ice or until it becomes lodged 
underneath the ice. Rivers wear away first the softer parts of the 
rock over which they flow, while glaciers wear away both hard and 
soft. Glaciers form moraines, rivers form flood plains, fans, and 
deltas. Rivers are frequently very important highways of commerce, 
while glaciers are obstructions. In what other ways do glaciers and 
rivers resemble each other and differ from each other? 

Glaciers form an important part in the freshwater circulation of 
the globe — a frozen portion of the circle, which checks and retards 
the rate but fortunately does not stop it entirely. If glacier ice did 
not move, it would be only a question of time until much of the surface 
moisture would accumulate on the high mountains and in the polar 
regions and thus be removed from circulation. 

313. Continental Glaciers. — In the geologic epoch im- 
mediately preceding the present, a large part of North America 
was covered with a great continental ice sheet which at its 
maximum covered about four million square miles. During 
its greatest extent this ice covered the northern United States 
north of the Ohio and Missouri rivers, and a large part of 
Canada. The ice spread out radially from three centers of 
accumulation : the Labrador center east of Hudson Bay, the 
Keewatin center west of Hudson Bay, and the Cordilleran 
center on the mountains of western Canada. There was 
possibly another center in or near Nova Scotia. (See Fig. 223.) 

There was a long period of growth, in which the snow continued 
to accumulate and the ice sheet continued to spread until it reached 
its greatest extent, then a longer period of decline, during which the 
ice sheet wasted away slowly until it was all melted. As with the 



GLACIERS 



325 



alpine glaciers, neither the growth nor the decline of the glacier was 
continuous, but there were periods of advance and recession. During 
the growth, each successive advance would carry the ice farther than 




Fig. 223. — The three glacial centers of North America : Labrador, La ; 
Keewatin, Ke ; and Cordilleran, Co. (After Chamberlin.) 



the preceding one until the maximum was reached, while during the 
waning period, successive recessions would make the ice sheet smaller 
until it' finally disappeared. At least five periods of extended ad- 



326 ELEMENTS OF PHYSICAL GEOGRAPHY 

vance and recession have been recognized in the record left in the 
deposits made by the glacier. The length of time from the beginning 
of this ice sheet until it disappeared must have been several hundred 
thousand years. The time since the North American continental 
glacier finally melted is variously estimated at from 20,000 to 50,000 
years, and by some even longer. One of the measuring rods used in 
determining the time interval since the final melting of the glacier 
is the Niagara gorge. (See Chapter VIII.) 

During or about the time of the existence of the continental glacier 
in North America there was one nearly as large in Europe. 




Fig. 224. — Hanging valleys in Quartz Creek Gorge, Mont. (Photo by U. S. 
Geological Survey.) 



In remote geologic ages of past time there have been continental 
glaciers in other portions of the world, in South America, in South 
Africa, and in India. 

314. Some of the Great Geographic Changes Produced by 
Continental Glaciers. — The geographic changes produced 
during the glacial period must have been many and some of 
them quite profound. Try to imagine the results of the move- 
ment of such an ice sheet over the country now ; its effect on 
the streams, lakes, hills, soil, vegetation, animals, and man. 
We can now study the results of this ice invasion as they ap- 



GLACIERS 327 

pear after an interval of thousands of years. What they were 
at the time we can try to picture in the mind. 

315. Erosion by Continental Glaciers. — Erosion by a con- 
tinental glacier must resemble in some ways erosion by an 
alpine glacier. It would be more widespread, since the ice 
covered the hills, mountains, and plains as well as the valleys. 
The ice was much thicker. It covered the higher portions of 
the Catskill Mountains, which are over 4000 feet high, and the 
high peaks of the Adirondacks, over 5000 feet, hence in the 
Hudson-Champlain Valley the ice must have been a mile or 
more in depth. 

The erosion was probably greatest in the valleys, as there 
the ice was thickest and moved faster. This resulted in deepen- 
ing and widening the north-south valleys. The ice coming 
from the north would move across the east-west valleys and 
tend rather to fill them up than to erode them deeper. This 
would result in many hanging valleys (Figs. 222 and 224). If 
the north-south valleys were worn deeper and wider and the 
tributary valleys from the east and west were not worn down, 
then after the ice melted, the floor of the tributary valley would 
be left hanging far above the floor of the main valley, forming 
waterfalls and cascades on the tributaries at the junction. If 
the tributary valleys were filled, the new drainage from the 
uplands would form even higher falls, where the streams poured 
over the bordering walls of the deeper main valley. Scores 
of such falls occur along the Finger Lakes and other north- 
south valleys in central New York. 

In many places, where the glacier flowed over a plain or 
nearly level region, it apparently did very little eroding, not 
even removing all of the mantle rock. In the hilly regions, 
not only the mantle rock was moved, but large quantities of the 
projecting bed rock were worn away. 

In regions of the more massive igneous and metamorphic 
rocks, ' the greater wear on the projecting points produced 



328 ELEMENTS OF PHYSICAL GEOGRAPHY 

numerous rounded or oval rock surfaces, known as the roches 
moutonnees or the sheep rocks. (See Fig. 217.) 

316. Striae, Grooves, and Polishing. — The erosion of the 
rock surface by a glacier is done by the rock material in the 
bottom of the ice. Where the material is sand and gravel, the 




Fig. 225. — Glacial strise on Round Hill, Catskill Mountains, 2400 feet above 
sea level. (Photo by H. D. McGlashan.) 



bed rock is marked by scratches called striae, since each sand 
grain or rock fragment pushed against the rock surface left a 
scratch (Figs. 225 and 226). 

The boulders or large rock fragments plowed deep grooves 
in the rock surface. The direction of the striae and grooves 
left on the rock surface indicates the direction in which the ice 
of the glacier was moving (Figs. 225 and 226). It is by means 



GLACIERS 329 

of the record left, by the striae that the three centers of glacia- 
tion were determined. The silt and fine mud in the bottom of 
the ice polished the surface over which they moved. 

The amount of erosion accomplished by the continental 
glacier would evidently be much greater towards the glacial 
centers and in general decrease towards the margin, which 




Fig. 226. — Glacial grooves on Vancouver Island, Victoria, B. C. Recently 
exposed by action of the waves on an advancing shore line. (Photo by the 
author.) 

accounts in part for the larger areas of ice-worn, bare rock 
surfaces of central and southern Canada and extreme northern 
United States than farther south. 

There is a difference of opinion among students of glacial phenomena 
about the actual amount of erosion of bed rock by the glacier. All 
agree that it eroded much, in many places all of the mantle rock, but 
some think that it eroded comparatively little of the bed rock, while 
others think it eroded vast quantities of the bed rock in many places. 



330 



ELEMENTS OF PHYSICAL GEOGRAPHY 



Where streams from the surface of the glacier poured down through 
crevasses, they eroded potholes in the bed rock underneath. Some of 
these glacial potholes are much larger than those formed in rapids in 
stream channels (Fig. 227). (See Sec. 271.) 

317. Transportation by the Continental Glacier. — The 
amount of material transported by the North American glacier 
must have been enormous. A large part of the mantle rock 




Fig. 227. — Glacial pothole in the Sierra Nevada Mountains, Calif. Show- 
ing the boulders used by the glacial waters in wearing the pothole. (Photo 
by U. S. Geological Survey.) 



over the vast area of millions of square miles was moved, some 
of it a short distance, some of it a long distance. In addition, 
the material eroded from the bed rock was carried away. 

Probably a smaller proportion of material was carried on 
the surface of the continental glacier than on an alpine glacier, 
since the continental glacier covered the hills as well as the 
valleys and there would be no rock cliffs above the glacier to 
furnish surface moraine. 



GLACIERS 



331 



A large part of the load was carried at the bottom of the glacier, 
partly frozen in the ice ; with that pushed along under and in front 
of the ice, it formed the ground moraine. By means of upward and 
cross currents in the ice much subglacial material became englacial 
by being carried up in the ice. By melting of the surface part of the 
glacier, toward the margin, some of the englacial material became 
superglacial or surface moraine. 




Fig. 228. — Glacial till or boulder clay. (Photo by the author.) 



318. Deposits Left by the Continental Glacier. — The ma- 
terial transported by the glacier was left on the surface when the 
glacier melted. Where it was distributed uniformly over the 
area it did not greatly change the topography; though the 
hills, valleys, and other surface features would have in some 
places a greater thickness of mantle rock than before, they 
would not be markedly different in size or shape. But the 
moraine was deposited irregularly; the surface after the 



332 



ELEMENTS OF PHYSICAL GEOGRAPHY 



glacier melted was quite different in its relief features from the 
surface on which the ice rested, which in turn was different from 
the surface before it was eroded by the glacier. 

319. Glacial Drift. — This is the name used to include all 
the loose rock material left on an area by a melted glacier. 
The word till is sometimes used with the same meaning. Some 




Fig. 229. — Drumlin, view looking east. North end of the drumlin steeper 
than the south end. (Photo by the author.) 



writers use till as synonymous with boulder clay, which is the 
ground moraine (Fig. 228) . 

320. Drumlins. — These are oval-shaped hills composed largely 
of boulder clay. They are accumulations of ground moraine 
formed under the glacier. They are elongated in the direction 
of the ice movement, and like the glacial striae serve to indicate 
the direction in which the ice moved at the place where they 
occur. Many drumlins are steeper at the north end than at 



GLACIERS 



333 



the south end. Drumlins occur in great numbers in central 
New York, between Syracuse and Rochester. There is an- 
other drumlin area in western New York, one east of Lake 
Ontario, one on the southern peninsula of Michigan, one in 
Wisconsin, and one near Boston, Massachusetts. (See Fig. 229, 
and the Weedsport, New York, contour sheet.) 

321. Terminal Moraines. — The terminal moraine and the 
terminal moraines of recession are conspicuous relief features of 




Fig. 230. 



Terminal moraine of recession of an alpine glacier, at Animas 
City, Colo. (Photo by U. S. Geological Survey.) 



deposits left by the continental glacier. As long as the edge 
of the glacier melted faster than the forward movement of the 
ice, the end of the margin of the glacier receded continuously 
and the moraine material was distributed more or less evenly 
over the surface. During periods when the rate of melting 
just balanced the rate of forward movement, the end would re- 
main stationary, and the terminal moraine would accumulate 
and form a hill or mass of morainal hills. The small basin-like 
depressions in the midst of the morainal hills are called kettle 



334 ELEMENTS OF PHYSICAL GEOGRAPHY 

holes. Some of them contain water and are called kettle lakes. 
Where the kettle holes or lakes are fairly abundant the moraine 
is called kettle moraine. (See Figs. 220 and 230, terminal 
moraines of an alpine glacier.) 

Lobate moraines were formed around the ends or margins of lobes or 
thumb-like projections of the edge of the ice. 




Fig. 231. — An esker, near Dayton, Ohio. (Photo by O. D. Von Engeln.) 

322. Glacio-fluvial Deposits. — Water flowing from the end 
of a melting glacier sometimes washed forward the moraine 
material and spread it over the area in front of the glacier, 
forming an outwash plain or frontal apron. Where it is washed 
down a valley it is called a valley train. 

Eskers are low winding ridges of gravel and sand formed, it 
is thought, by accumulations in the courses of streams that 
flowed underneath the glacier (Fig. 231). 

Karnes are gravel and sand hills formed at or near the mar- 
gin of glaciers. Karnes resemble eskers in being composed 



GLACIERS 335 

of partially stratified sand and gravel, but differ from them in 
being more irregular in size, generally higher and shorter than 
eskers. Karnes are frequently transverse to the direction of 
the ice movement while eskers more commonly trend in the 
same direction as the moving ice. Drumlins differ from both 
kames and eskers in being regular and symmetrical in shape 
and size and consisting of unstratified boulder clay or till. 
(Fig. 232.) 




Fig. 232. — Kames, near Mendon,' N. Y. (Photo by H. L. Fairchild.) 

323. Erratics. — Erratics, boulders composed of fragments 
of rock unlike the underlying bed rock, characterize glacial de- 
posits in many places. These boulders, which have been trans- 
ported on and in the glacier, are left on the surface of the 
earth, along with the other rock material, when the ice melts. 
Perched boulders or rocking stones are large erratics insecurely 
perched on the bed rock in a more or less balanced position. 
Erratics should not be confused with the common boulders of 
disintegration, which are residual fragments of the underlying 
bed rock (Figs. 233 and 234). 

324. Glacial Stream Channels. — In the region covered by 
the continental glacier there are many deep channels cut in the 
rocks by waters diverted from their former channels by the 



336 



ELEMENTS OF PHYSICAL GEOGRAPHY 



ice. The glacial lobe that extended down the Okanogan Valley 
in Washington formed an ice dam across the Columbia River 
Valley. Above the dam the waters overflowed across the 
Columbia Plateau into the valley many miles below, cutting 
a deep canyon. When the end of the Okanogan glacier melted 
out of the Columbia Valley, the Columbia waters flowed in 




Fig. 233. 



Perched glacial boulder (erratic) in Yosemite National Park, 
Calif. (Photo by U. S. Geological Survey.) 



their former channel. The abandoned channel across the 
plateau is called the Grand Coulee. There are other similar 
but smaller coulees in the same region. 

In central New York where the glacier moving south formed a dam 
across all the streams flowing north, the waters from behind the dam 
overflowed and cut deep channels across the divides. When the ice 
melted the streams resumed their old channels and abandoned the 
glacial stream channels. Where these glacial streams flowed over 
the edge of a cliff into the next valley, waterfalls were formed. The 



GLACIERS 



337 




Fig. 234. 



Boulders of disintegration; compare with glacial boulder in 
Fig. 233. (Photo by U. S. Geological Survey.) 



338 



ELEMENTS OF PHYSICAL GEOGRAPHY 



recession of such falls formed gorges like that at Niagara. When 
the streams abandoned the glacial channels the plunge basins at the 
bottom of the falls formed small lakes called plunge basin lakes. There 
are scores of these glacial stream channels along the northern edge of 
the Allegheny Plateau through central New York. An area inclosing 
one of the best of these channels and lakes near Syracuse, New York, 
is now a New York State park (Fig. 235). 




Fig. 235. — View in glacial channel near Jamesville, N. Y. 

author.) 



(Photo by the 



325. Glacial Lakes and Waterfalls. — It is estimated there 
are more than 10,000 lakes in the state of Minnesota. There 
are probably more than 50,000 in the glaciated area of the 
United States and Canada. Practically all of these are due 
to the occurrence of the glacier. Some were formed by the 
erosive work of the ice but more of them were formed by the 
moraines. Besides the existing lakes, there were many others 
formed by the glacier while it was present, that disappeared 
when the ice melted. In addition a great many small glacial 



GLACIERS 



339 




Fig. 236. — Lake Ellen Wilson, a glacial lake, at Gunsight Pass in Glacier 
National Park. (Photo copyrighted by R. E. Marble, 1914.) 



340 ELEMENTS OF PHYSICAL GEOGRAPHY 

lakes have been filled up and destroyed since the ice melted 
(Figs. 236, 238, 239, and 240). 

To the glacier we owe nearly all the hundreds of waterfalls 
of Canada and northern United States. 

326. Economic Effects of the Glacier. — Many of the changes 
produced on the geography of the northern United States by 
the continental glacier have had their influence on man and his 
industries. Some of the effects have been beneficial and some 
otherwise. 

(1) The general effect of the glacier on the topography was 
to make it more regular. Locally some valleys have been 
deepened, but over the entire area the amount of material de- 
posited in the valleys exceeded the amount eroded. Drumlins, 
kames, eskers, and terminal moraines have formed many small 
hills, but erosion and filling has probably obliterated more hills 
than were formed. A region known as the " driftless area " 
along the Mississippi River in Wisconsin and Iowa, that was 
not covered by the glacier, is much more rugged than the sur- 
rounding drift-covered areas. Central and southern Indiana 
south of the glacial area is more rugged than the glaciated area. 

(2) The glacial deposits on the whole have a more productive 
soil than the original residual soils, because they are composed 
of a mixture of rock materials from many localities, and con- 
tain more elements of fertility. Locally, sand, gravel, and 
boulder deposits are less productive than the original soils, 
but these areas are small compared with the more extensive 
till soils. In the driftless area above cited, the value of the 
agricultural products is much less than that of an equal area 
on the bordering glaciated region. 

(3) Numerous lakes cover large areas that might otherwise 
be used for farming purposes. However, the lakes are not 
valueless. The Great Lakes form one of the finest water high- 
ways in the world and carry a vast commerce. They supply 
large quantities of food fishes. They furnish a splendid supply 



GLACIERS 341 

of pure water to near-by cities. They temper the climate of 
the bordering lands, adding to the value of the fruit and farm 
crops. They serve as regulators to the numerous streams of the 
area, preventing disastrous floods and keeping up the supply 
of water power during the dry seasons. They make excellent 
sites for cities and summer cottages. 

(4) Numerous swamp areas produce much waste lands, but 
there is a partial compensation for this loss in the great produc- 
tivity of the swamp lands that have been drained and brought 
under cultivation. They have very fertile soils. Some of the 
swamp lands are covered with productive forests. Some are 
utilized in growing cranberries. 

(5) Numerous waterfalls produced by glacial action are not 
only objects of beauty, but sources of unlimited power which 
is becoming more valuable each year as the coal supply de- 
creases. 

(6) The vast supplies of sand and gravel in the kames, eskers, 
terraces, and lake shores are proving valuable in building and 
construction work of all kinds. 

(7) Clay deposits left by the glacier and the glacial waters, 
are used in large quantities for making brick, terra cotta, and 
other clay products. 

The spread of the great ice sheet over northern United States and 
Canada destroyed practically all the vegetation of the glaciated area 
at that time, but it left the region more valuable to the present plants 
and to man and other animals than it was before. The richest and 
most populous portions of the United States are in the glaciated areas 
of the north, although the south was settled first. This may not be 
due entirely to the effect of the glacier, but the glacier appears to have 
been an important factor. 

327. Causes of the Glacial Period. — The occurrence of a con- 
tinental glacier in a region where there was none before and is none 
now necessitates a change in climate, in fact two changes, one to pro- 
duce the glacier and one to cause its disappearance. The probable 
causes assigned for these changes are: (1) An elevation of the land 



342 



ELEMENTS OF PHYSICAL GEOGRAPHY 



to higher and colder altitudes to produce the glacier, followed by a 
depression to cause its melting. (2) A change in the earth's orbit 
accompanied by a shifting of the earth's axis. (3) A decrease in the 
amount of carbonic acid gas in the atmosphere to produce a colder 
climate, and a subsequent increase to bring about warmer conditions. 
A discussion of this topic belongs to geology rather than geography. 




Fig. 237. 



Small icebergs in Iceberg Lake, Glacier National Park, Mont. 
(Photo by Winter Photo Co.) 



328. Icebergs. — Icebergs are floating masses of ice broken 
off from the ends of glaciers which enter the sea. They occur 
only in high latitudes, because in low latitudes the glaciers are 
melted before they get down to sea level. The largest bergs 
come from the Antarctic continental glacier in south polar 
seas. Large ones are formed where the Greenland glaciers 
enter the sea. Some of the Greenland icebergs drift south 
as far as the path of the transatlantic steamships, where they 



GLACIERS 343 

prove a menace to commerce. The sinking of the great steamer 
Titanic was caused by its collision with an iceberg that had 
drifted down from Greenland. 

The movements of icebergs are influenced to some extent 
by the winds, but probably more by the ocean currents as a 
large part of the bergs is below the water. They drift south 
in the Atlantic with the cold Labrador Current. The rock 
material carried by the icebergs is dropped on the ocean bottom 
as the bergs melt. 

Similar but small icebergs are formed by the alpine glaciers 
where they enter the lakes as in Iceberg Lake in Glacier Na- 
tional Park (Fig. 237). 

QUESTIONS 

1. State the necessary conditions for a snow field. 

2. Name and locate all the mountain regions that have glaciers. 

3. Why are there no glaciers on the Adirondack Mountains ? On 
the Boston Mountains ? 

4. Where do continental glaciers occur now? Where have they 
occurred in the past ? 

5. How does a valley through which a glacier has moved differ 
from a river-formed valley? 

6. Compare an alpine glacier with a river in all points of re- 
semblance, in all points of difference. 

7. By examining the terminal moraine of an alpine glacier could 
you tell whether the glacier had recently been advancing or receding? 
How? 

8. Why do so many of the cirques of former alpine glaciers con- 
tain lakes ? 

9. Explain how high mountains would differ in appearance from 
the present if glacier ice did not move. 

10. Suppose the climate should change now to the same as at the 
beginning of the Glacial Period, should you recognize the change? 

11. Many people lived a lifetime in the Alps Mountains and did not 
know that the ice in a glacier moved. Do you think that you would 
know that the ice moved if you lived near a glacier for a few years ? 
How? . 

12. During the Revolutionary War no one in the United States 



344 ELEMENTS OF PHYSICAL GEOGRAPHY 

knew that there had been a glacier over New England and New York. 
If you had been living at that time with your present knowledge, how 
could you have convinced the people that a glacier had been there? 

13. Explain how hanging valleys are formed. 

14. Study a contour map of a drumlin area (the Syracuse, or Bald- 
winsville, New York, or some other) and determine the direction in 
which the ice was moving when the drumlins were formed. 

15. How can you distinguish a drumlin from a kame? A kame 
from an esker? What economic use is made of some kames andeskers 
that occur near cities ? 

16. The stone fences of New England and New York are different 
from those in central or southern Pennsylvania. Why? There 
are more of them. Why? 

17. How does a rocking stone left by a glacier differ from one left 
by disintegration? 

18. Make a list of all the ways in which glacial lakes are of use to 
man. 

19. What evidence can you cite that most of the soil left by the 
continental glacier is better than the soil removed by the glacier ? 

20. State the kinds of glacial deposits that are probably less valuable 
than the original soil. 



CHAPTER X 
LAKES AND SWAMPS 

Lakes are important geographic features. In general they 
are more passive forms of water than rivers, glaciers, and oceans. 
Their activities are confined almost entirely to the work of the 
waves on the shore. They serve as catch basins for the dep- 
osition of sediment and for the accumulation of vegetable and 
animal deposits. Lake plains are formed when the basins are 
filled up or drained. Almost all the shore features of the ocean 
described in Chapter IV are duplicated on a smaller scale 
on lake shores, and most of the wave work described in that 
chapter is equally applicable to the lakes. The principal 
difference is the absence of tides on the lakes. The ocean be- 
ing the larger body of water has larger waves; salt water 
being denser, the waves are heavier. 

329. Definition of Lake. — Lakes are basin-shaped bodies 
of comparatively quiet waters on the continents and islands. 
They are mostly fresh water, but in arid regions many of them 
are salt or alkaline. The smaller water bodies are sometimes 
called ponds, but the distinction between pond and lake is 
purely an arbitrary one and largely local. In some portions 
of the country the smaller bodies of water are all called ponds, 
in other places they are called lakes. The larger salt water 
lakes are sometimes called seas, as the Caspian Sea and Dead 
Sea. The bodies of standing water formed by man are con- 
monly called dams or reservoirs. They are not essentially 
different from lakes except in origin. 

345 



346 ELEMENTS OF PHYSICAL GEOGRAPHY 

Most lakes are permanent, but there are some temporary lakes 
which contain water during the wet season, while during the dry season 
the water evaporates or sinks into the earth. The permanent lakes 
are those in which at least part of the basin extends below the 
permanent water table. Most of the small lakes in arid regions 
are temporary lakes whose basins lie above the permanent water 
table. 

330. Variation of Lakes in Size. — Many small lakes and some 
large ones vary greatly in size from season to season. Lake Tchad, 
in Africa, has an area of about 40,000 square miles in the wet season, 




Fig. 238. — Glacial lakes in the Adirondack Mountains. View from St. Regis 
Mount. (Photo by S. R. Stoddard.) 

but dwindles to 6000 in dry weather. Quin Lake on Black Rock 
Desert in Nevada covers more than 400 square miles in wet seasons, 
but dries up entirely in dry seasons. It is never more than a few 
inches deep. Lake Tulare in California some years ago became so 
small that hundreds of acres of its former lake bed were cultivated. 
The dry period was followed by a wet one in which the lake waters 
again spread over the farm lands. 

The conditions necessary for a lake are a basin-like depression and 
sufficient precipitation to fill or partly fill the basin. If the bottom 
of the basin is below the permanent water table, it is a permanent lake, 
if above the water table, it is a temporary lake ; if the lake basin is 



LAKES AND SWAMPS 



347 



shallow and only a small part of the basin is below the water table, the 
lake varies greatly in size with the seasons. 

Temporary fluctuations of lake levels are produced by winds and 
atmospheric pressure. A strong wind in one direction for several 
days causes a rise in level on the windward shore and a subsidence on 
the lee shore. A strong west wind has been known to cause a rise of 
several feet at the east end of Lake Erie and high water in the Niagara 




Fig. 



239. — ■ Glacial Lake Chelan in the Cascade Mountains, Wash, 
by a large alpine glacier ; bottom of the lake below sea level. 



Formed 



River. A strong anticyclone or high pressure area at one end of one 
of the Great Lakes causes a marked depression of the lake level and a 
rise of level at the opposite end. 

331. Distribution of Lakes. — Most lowland lakes occur on 
river flood plains, deltas, or along the coast. Most of the up- 
land lakes are directly or indirectly of glacial origin, and occur 
in regions formerly covered by a glacier. Hence, the im- 
portant lake regions of North America are the glaciated areas 



348 



ELEMENTS OF PHYSICAL GEOGRAPHY 



of Canada and of northern United States (Fig. 238), the western 
mountains, the Mississippi flood plain and delta, and the south 
Atlantic and Gulf coast. Secondary lake regions are the 
Florida peninsula, where there are many structural and solu- 
tion basins in the limestone, the Great Plains along the eastern 
base of the Rocky Mountains, and in structural and wind erosion 




Fig. 240. 



Glacial Lake Brainerd, in the Rocky Mountains, Colo., near the 
continental divide. (Photo by the author.) 



basins in the Great Basin between the Rocky and Pacific 
Mountains. 

The uplands of eastern and central United States, south of 
the glaciated area, are almost devoid of lakes. 

The reason for this distribution is found in the fact that all lakes 
are young in comparison with other geographic features, such as river 
valleys, mountains, and plains. Hence on areas which have not re- 
cently been covered by a glacier or acted upon by water, as on the 



LAKES AND SWAMPS 



349 



shores or flood plains, or by winds, as in arid basins, the lake basins 
have been destroyed by erosion ; that is they have been filled up or 
drained. 

332. Origin of Lakes. — (1) Glaciers form lakes : (a) by 
erosion in the bed rock, especially so in cirques or snow basins 
at the head of Alpine glaciers, (6) by moraines across stream 



: ■ ' . _ . •■■■:■...■.■■■..■■■,.. ■•-■■. - 




Fig. 241. — Galveston Bay, Tex. The delta of Trinity River will in time 
extend to the south shore, when Turtle Bay will become a lake. 



valleys, such as the Finger Lakes of New York, (c) by kettle 
holes in a moraine, called kettle lakes, (d) in plunge basins at 
the base of extinct waterfalls, or on the course of glacial streams. 
(See Chapter IX, and Figs. 239 and 240.) 

(2) Rivers form lakes on flood plains : (a) by cutting off 
meanders : oxbow lakes ; (6) by a tributary building an alluvial 



350 



ELEMENTS OF PHYSICAL GEOGRAPHY 



fan across another river, as the alluvial fan of Kings River 
extends across the San Joaquin Valley, forming Lake Tulare ; 
(c) by building a natural levee or bar across the mouth of a 
tributary, as the levee lakes of the lower Red River in Louisiana ; 




Fig. 242. — Contour map of Crater Lake, Ore. A caldera lake formed by 
the sinking of the top of Mt. Mazana into the crater of the volcano. Numbers 
on lake represent depth of the water. (Copied from TJ. S. Geological Survey.) 

(d) by building a delta across a bay or estuary : thus the delta 
of the Colorado River across the Gulf of California cut off the 
Salton Lake basin at the north end, and Trinity River is now 
extending its delta across Galveston Bay, and when the end of 
the delta reaches the opposite shore the head of the present 



LAKES AND SWAMPS 351 

bay will be a lake (See Fig. 241) ; (e) the shifting of distribu- 
taries on a delta sometimes leaves lakes in portions of aban- 
doned channels. 

(3) A depression of a portion of the earth's surface by fractur- 
ing or bending sometimes produces a lake basin. The large 
lakes along the Great Rift extending north and south through 
Africa are thought to have been formed in this way ; Reelsfoot 
Lake in western Tennessee and Owens Lake in California were 
formed by depressions accompanying earthquakes. Lake 
Superior basin was probably formed in part by the down- 
warping of the lake bottom, although erosion and deposition 




Fig. 243. — Cross section through Crater Lake and Wizard Island. 

by the glacier were probably important factors. Several lakes 
occur in depressed areas in the Selkirks and Rocky Mountains 
of British Columbia. 

(4) Volcanoes form lakes : (a) where a stream of lava builds an 
obstruction across a river valley, (b) in the craters or calderas of ex- 
tinct volcanoes, such as Crater Lake in Crater Lake National Park, 
in the Cascade Mountains of Oregon. Crater Lake is nearly 2000 
feet deep and the bottom nearly 4000 feet below the top of the moun- 
tain (Figs. 242 and 243). 

(5) Landslides and avalanches form lakes : (a) by the obstruction 
built across the valley. In 1893 a landslide in the Himalaya Moun- 
tains carried about 800,000,000 tons of rock material into the valley 
of a tributary of the Ganges River, forming a dam 1000 feet high and 
a lake four miles long. Further, (b) during the landslide at Frank, 
Alberta, about 70,000,000 tons of rock fell from the end of Turtle 
Mountain with such force as to scoop out a lake basin at the bottom 
of the mountain. 

(6) Many "beaver lakes" were formed in northern United States 
and Canada by beavers building dams across stream channels 
(Fig. 244). 



352 



ELEMENTS OF PHYSICAL GEOGRAPHY 



(7) Sink hole lakes are formed in limestone regions where the open- 
ing in the bottom of the sink becomes stopped so that the water cannot 
escape. In the limestone regions of Kentucky and Indiana, where 
there is a scarcity of surface waters, the farmers supplement the work 
of nature by stopping the openings in the bottoms of the sink holes that 
are not stopped by natural agencies. Many of the numerous lakes of 




Fig. 



244. — Small lake in Rocky Mountains, formed by beavers. 
U. S. Biological Survey.) 



(Photo by 



Florida are solution basins in limestone, although many of the larger 
ones are due in part to sinking or down-warping of the bed rock. 

There are some lake basins formed in other ways. Try to classify the 
lakes you know, and see in which of the foregoing classes they belong. 

333. How Lakes Disappear. — Rivers are said to be the 
natural enemies of lakes. They exercise a destructive action 
in two ways. The sediment washed into the lake by the rivers, 



LAKES AND SWAMPS 



353 



in time fills the lake basin. The stream flowing from the lake 
lowers the outlet and drains the lake. Of the two, the first is 
more destructive than the second. Nearly all the sediment 
carried into a lake by the rivers is deposited, because the stand- 
ing water of the lake checks the velocity of the inflowing river, 
and the lakes thus become settling tanks for river sediment 
(Figs. 245 and 246). 

The Great Lakes 
are filling very 
slowly in this way 
because the streams 
flowing in are com- 
paratively small 
and carry but little 
sediment. The 
drainage area on 
the south side of 
all the Great Lakes 
except Ontario is 
small and the rivers 
short and of low 
grade. On the 
north side of the 
lakes the streams 
have high grades, 
but they flow from the forested region of Ontario, where they 
obtain but little sediment, and many of them pass through 
smaller lakes which filter the sediment from the streams. 

The Finger Lakes of central New York are filling much faster. 
Although the inflowing streams are small, they flow down 
steep slopes over soft rocks and carry much sediment. The 
delta plains at the heads of all these lakes, varying from a mile 
to several miles in length, represent portions already filled. 
Even the small streams flowing in at the side are building deltas 




Fig. 245. — Lakes form settling tanks for the 
sediment carried in by rivers, until the lake becomes 
filled. (See Fig. 246.) 



354 



ELEMENTS OF PHYSICAL GEOGRAPHY 



rapidly in proportion to the size of the streams. In addition 
there is the mud washed beyond the delta and that washed 
from the shore by the waves. (See Plate I, Chapter I.) 

334. Other Factors in Destroying Lakes. — The lowering of 
a lake level by the cutting down of the outlet becomes im- 
portant only where the stream flows over loose material, such 

as sand, gravel, or 
mud deposits. 
Thus, lakes formed 
by landslides and 
avalanches are fre- 
quently destroyed 
in this way. Where 
the outlet stream 
flows over hard 
rock, as do the St. 
Lawrence and the 
Niagara and " Soo " 
Rivers, the lower- 
ing of the outlet is 
imperceptible, as 
clear water does not 
wear away hard 
rock. 




Fig. 246. — After the lake basin is filled, the outlet 
stream is supplied with sediment, degrades its channel, 
and then picks up and carries to lower levels the 
lake deposits. (See Fig. 245.) 



Other factors that 
aid rivers in destroy- 
ing lakes are the action of the waves on the shore, and the action of 
the wind in carrying dust, sand, and other materials. This becomes 
an important factor in desert regions and along sandy coast areas. 
Organic agencies, such as deposits of shells and plants forming marl 
beds, and deposits of plant remains forming muck and peat deposits, 
help fill lake basins, markedly so in many shallow lakes. Hundreds of 
small lakes that have no streams flowing in and some of them no sur- 
face streams flowing out are rapidly filling up with marl and muck 
deposits ; while hundreds of others in the glaciated area of the United 



LAKES AND SWAMPS 



355 



States and Canada have been filled. Some of them are now swamps, 
some grass flats or meadows, some are forested, and many of them are 
under cultivation (Fig. 247). 

By a change of climate lakes disappear by evaporation. This, how- 
ever, does not destroy the basin, and when the climate again becomes 
humid the basin will once more contain a lake. 




Fig. 247. — Upper Ausable Lake, N. Y. The lake is being filled by vegetable 
matter. Notice the zonal arrangement of the vegetation. The shrub area at 
the sides on the filled portion of the lake is extending towards the center. The 
bordering forests are encroaching on the shrub area. (Photo by S. R. Stoddard.) 

335. Fossil or Extinct Lakes. — Areas formerly covered by 
lakes which have been drained or filled, may be called fossil 
lakes. A fossil lake may be recognized by : (1) characteristic 
shore features, such as cobble or gravel beaches, sand and 
gravel terraces, shore cliffs, etc., (2) lacustrine plains bordered 
in part at least by shore features — such as the great wheat 
region in the Red River valley in North Dakota, Minnesota, 
and Manitoba. 



356 ELEMENTS OF PHYSICAL GEOGRAPHY 

Lake Ontario occupies part of the basin of fossil Lake Iroquois, 
which extends as far east as Little Falls on the Mohawk River, and as 
far south as Syracuse, New York. 

Great Salt Lake, Utah Lake, Sevier Lake, all occupy depressions in 
the floor of fossil Lake Bonneville, which formerly covered a large 
area in northwestern Utah. 

336. Life in Lakes. — - Lakes, except the salt and alkali 
ones, contain many forms of animal and vegetable life. The 
animal life is probably more prolific in the larger lakes and 
the vegetable life more abundant in the smaller and shallower 
lakes. As already stated, many of the smaller lakes terminate 
by being filled with the accumulated remains of animals and 
plants. 

Some of the animals, such as eels and salmon, spend part 
of their existence in salt water and part in fresh ; but with 
a few exceptions of this kind, the life, both animal and plant, 
in lakes is decidedly different from that in the sea. Life in 
the sea is more varied and locally more prolific than in the 
lakes. 

337. Diatoms. — There is one class of exceedingly small micro- 
scopic plants, known as diatoms, that occurs in great abundance in 
lakes as well as in streams and the ocean. Although they are found 
in many lakes and streams, the largest deposits occur in the ocean. 
The diatoms are composed of opal, that is, silica combined with water. 
So small are these plants that about four billions of them are contained 
in a cubic inch. Yet so numerous" are they that in some places they 
form deposits many hundreds, even thousands, of feet in thickness. 
The material composed of diatoms is known as tripoli or diatomaceous 
earth, sometimes called infusorial earth. It is so light and porous that 
when dry it floats on water. It is used as a polishing powder, as a 
filler for soaps, as an absorbent for nitroglycerin in making dynamite, 
and as fireproof material in buildings. A slippery brown material 
that covers stones in the brooks in many places, is composed of diatoms. 
(Fig. 248.) 

Diatoms form deposits from a few feet to 20 feet or more in thick- 
ness in many shallow lakes in the northern United States. Shallow 
Pond, near Wanakena, New York, contains a thick deposit of nearly 



LAKES AND SWAMPS 



357 



pure diatomaeeous earth. In many of the lakes the diatom deposits 
are mixed with so much muck and marl that the diatoms are ob- 
scured. There is a deposit more than 20 feet thick near Richmond, 
Virginia. 



w 




Fig. 248. — Micro-drawing of diatoms, microscopic plants that secrete 
silica, the accumulated remains of which form thick beds in lakes and oceans, 
(Drawing by W. F. Prouty.) 



Probably the largest deposits of diatoms occur in California and 
Nevada. At Lompoc, California, nearly pure diatomaeeous earth 
forms a bed more than 1000 feet thick over an area of hundreds of 
square miles. Much of the oil in California occurs in porous dia- 



358 ELEMENTS OF PHYSICAL GEOGRAPHY 

tomaceous beds. It is estimated that an area of more than 10,000,000 
square miles of the sea bottom is covered with diatomaceous deposits. 
(See Fig. 47.) 

338. Functions of Lakes. — Lakes have a number of impor- 
tant functions which make them useful to man in several ways. 

(1) They serve to regulate the run-off from the rains and 
melting snows, preventing destructive floods in the wet season 
and keeping up the flow of streams in dry seasons. The St. 
Lawrence River, because of the many lakes in its upper basin, 
is never subject to destructive floods. The Ohio River and its 
tributaries, with no lakes to hold the flood waters, are subject 
to disastrous floods which destroy much property in the valleys. 
The Ohio River in flood season rises fifty to sixty feet above 
low water stage, while the St. Lawrence rarely rises as many 
inches. The people of Dayton and other towns in the Miami 
River valley are now constructing reservoirs or artificial lakes 
to prevent a recurrence of the great flood that destroyed so 
much property in that valley in the year 1913. 

The regulation of the run-off greatly aids commerce on the 
rivers. Nearly all the large tributaries of the Mississippi 
River carry enough water during the year to make them good 
boat routes, but lacking lakes to control the waters, they have 
too much water in flood season and too little in dry seasons. 
Furthermore the changes made by erosion and deposition by 
the flood, make it expensive to keep a continuous channel deep 
enough for steamers. This drawback is remedied to some ex- 
tent on the Monongahela and upper Ohio Rivers by construct- 
ing dams, thereby making artificial lakes, but the dams are 
not yet large enough to hold the flood waters. 

(2) Lakes furnish a valuable supply of excellent water for 
use in cities. The cities on the Great Lakes and those near 
the Finger Lakes are especially favored in this respect. New 
York City has expended over 160 million dollars in construct- 
ing an artificial lake, the Ashokan Dam, in the Catskills, because 



LAKES AND SWAMPS 359 

there is no natural lake of sufficient size, accessible for the city 
water supply. 

Los Angeles has expended many millions of dollars building 
a pipe line and canal system to carry the water from a lake 
in the Sierra Nevada Mountains 150 miles away. The line 
is carried across a desert and two ranges of mountains. 

(3) Lakes form valuable natural highways for commerce. 
The Great Lakes with the intersecting rivers and canals form 
one of the greatest commercial highways in the world. Many 
smaller lakes are utilized in a similar way on a smaller scale. 

(4) Lakes serve to temper the climates of the lands border- 
ing them, especially on the lee side. Since water absorbs heat 
less rapidly and loses it more slowly, the lakes are warmer in 
winter and colder in summer than land areas, and thus temper 
the winds that blow across them. 

(5) Fish obtained from the lakes are an important addition 
to the food supply of the country. The Great Lakes, the 
Finger Lakes, and some of the other larger lakes support a 
fishing industry. Fishing in most of the smaller lakes is a 
recreation rather than an industry, but whether the fish are 
taken for profit or pleasure, the food value is the same. 

339. Life History of Lakes. — ■ Like other natural phe- 
nomena, a lake has a period of growth, maturity, decline, old 
age, and death, which may be termed its life history. This is 
not uniform, but varies with different classes of lakes. The 
greatest variation is between lakes in dry and those in moist 
climates. In moist climates the average age of a lake is not 
long in comparison with the life of a river or mountain, but 
much longer than the life of any animal or plant. 

Lakes may come into existence in any one of the several ways 
mentioned in the preceding pages. With the exception of a 
very few lakes that have been blown up by volcanic explosions, 
they are destroyed slowly by the combined action of the different 
agencies previously described. When a lake basin is filled, the 



360 



ELEMENTS OF PHYSICAL GEOGRAPHY 



lake disappears as a body of water and streams meander across 
the fertile plain formed of lake deposits. In course of time the 
stream leading away from the old lake basin will lower its 
channel, because it now carries sediment which was formerly 
deposited in the lake. This will cause the streams flowing 
over the plain of the lake-filled basin to quicken their velocity 
and hence erode the soft materials, finally carrying away all 
the deposits that filled the lake, thus destroying the last vestiges. 
The streams on the Fargo, North Dakota, topographic sheet 
are flowing over a lake-filled plain and are just beginning the 
work of carrying away the sediment. (See Figs. 245 and 246.) 




^ ^jglglpp"! 



1,000 




Fig. 249. — Diagram showing comparative depths of the Laurentian Great 
Lakes. The bottom of four of them extends below sea level. 

A lake is thus seen to be an incident in the life of a river 
which deposits in the lake the load of sediment it is carrying 
from the mountains to the sea. At a later period, after having 
filled the lake basin, it again takes up the sediment and carries 
it on to the next stopping place and finally to the sea. 

Many small lakes have a different history from the above, because 
they have scarcely any sediment carried into them ; in fact, there are 
many small lakes that have no surface streams flowing into them and 
either no stream or else a very small sluggish stream flowing out. 
(See Fig. 238.) Such lakes will be filled in time by the remains of 
plants and animals that grow and die in the lake. Such a lake forms 
first a swamp, which later becomes firm land and forms a meadow, 
which in turn is covered with forest or utilized as farm land. There 
are no deltas, beaches, or evidences of wave action in most of these 
small muck- and marl-filled lakes. 



LAKES AND SWAMPS 



361 



Brief History of the Laurentian Great Lakes. — The chain 
of lakes along the northern boundary of the United States 
includes five of the world's great fresh-water lakes. One of 
them, Lake Michigan, lies wholly in the United States, the other 
four lie on the boundary between this country and Canada. 
They are of special interest because of their great size and the 
fact that they are connected, which makes them the greatest 
inland commercial highway in the world. (Fig. 249.) 




Fig. 250. — One stage in the history of the Great Lakes. (Taylor.) 

The tonnage of freight passing annually through the " Soo " 
locks at the outlet of Lake Superior is greater than that through 
New York Harbor or any of the great harbors of the world, 
despite the fact that the lake route is closed three months in the 
year because of ice. The principal items of freight on the Great 
Lakes are iron ore from the Lake Superior iron ore district to 
the lower lake points for the furnaces of Pennsylvania, New 
York, Ohio, Indiana, and Illinois ; wheat, corn, oats, and other 
grains from the rich agricultural regions of the Middle West to 



362 



ELEMENTS OF PHYSICAL GEOGRAPHY 



the markets of the East ; and lumber from the northern forests 
to the lower lake ports. The west-bound traffic on the lakes, 
which is less than the east-bound, consists chiefly of coal and 
goods from eastern factories to the farming districts of the west. 

The origin of these Great Lakes is involved in the history of the 
North American Continental Glacier. Before the advent of the 
glacier these lakes were not in existence. It is probable that they 
now occupy areas that were parts of one or more river valleys before 




Fig. 251. — - Glacial Lake Iroquois. The water of the Ontario lake basin 
then drained through the Mohawk Valley because the glacier blocked the out- 
let through the St. Lawrence Valley. (Map by Gilbert.) 

the glacial period. The movement of the glacier widened and deepened 
the valleys in some places and deposited moraines in others, thus form- 
ing inclosed lake basins in what were formerly open river valleys. 

During the melting away of the glacier the ice melted first from 
the south end of each of the lake basins, while the northern ends were 
still filled with ice. The lakes first formed in these depressions grew 
in size with further melting of the ice, until the entire basins were 
filled with water instead of ice. The drainage of the first-formed 
lakes was west into the Mississippi River as the present outlet through 
the St. Lawrence River was still filled with ice. Part of the time the 
drainage was through the Mohawk Valley into the Hudson River. 
At one period in their history the drainage of the upper lakes was 



LAKES AND SWAMPS 



363 



through the Trent River in Ontario and again for a time through the 
Ottawa River (Figs. 250 and 251). 

The position and former extent of many of the now extinct glacial 
lakes is known from study of the remnants of the fossil shore lines 
surrounding the present Great Lakes. The history of the lakes is 
complicated by the warping of the earth's surface during this period. 
In fact the warping movement is still in progress. At one period 
following the melting of the ice from the St. Lawrence Valley, the 
sea extended up that valley, probably into Lake Ontario, but certainly 
into Lake Champlain, which was then an arm of the sea. 

Area, Depth, and Altitude of the Laurentian Great Lakes 
with Some op the Other Great Lakes of the World for 
Comparison 



Area in Square 
Miles 



Maximum 
Depth 



Altitude op Sur- 
face Above Sea 
Level 


602 


581 


581 


573 


247 


7,738 3 
1,079 
6,225 3 


6,239 3 
444 


-85 i 


1,700 3 


3,800 
1,500 
12,500 3 
710 


573 


900 


650 


-1300 1 



Superior 

Michigan 

Huron 

Erie 

Ontario 

Yellowstone .... 

Chelan 

Tahoe 

Crater 

Seneca (Finger Lake) . 
Caspian (salt) . 

Baikal 

Victoria Nyanza 

Nyassa 

Titicaca 

Winnipeg 

Great Bear .... 

Chad 

Como 

Dead Sea (salt) . . . 



. 31,200 

22,500 

22,320 

9,960 

7,240 

140 

85 

220 

25 

67.7 

170,000 

13,000 

26,000 

10,200-14,200 2 

3,200 

9,400 

11,200 

6,000-40,000 2 

60 

340 



1,008 
870 
700 
200 
738 

1,500 
1,635 
2,000 

618 
3,200 
5,618 

240 
2,300 

700 
70 

200 
8-20 
1,340 
1,278 



1 Below sea level. 

1 Dry season and wet season areas. 

3 Lake Titicaca is the highest large mountain lake ; Yellowstone, Crater, 



364 



ELEMENTS OF PHYSICAL GEOGRAPHY 



340. Lakes in Arid Regions. — In arid regions the life history 
of a lake is somewhat different, being in general longer and more 
complex than in a humid region. In an inclosed basin area, the lowest 
depressions will have no outlet and hence cannot be destroyed by drain- 
ing. The sediments and salts carried in and deposited, raise the lake 
bed, but this in turn raises the level of the water and causes it to spread 
out over a greater area. But increased area means increased evapora- 
tion and hence the lake increases or diminishes as the case may be, 
until the evaporation equals the inflow. The lake will be subject to 




Fig. 252. — Alkali lake on the Laramie Plains, Wyo. (Photo by U. G. Cornell.) 

many vicissitudes with change of climate, until it finally ends in one 
of two ways : (a) aridity may increase until the lake dries up and 
disappears as such, pending another change in climate ; or (b) the 
humidity may increase until the entire basin fills up and overflows, 
when it ends as any other lake in a humid region. A lake may become 
salt in a humid region by being depressed below sea level, where the 
sea water has access to the basin ; it then becomes for the time an 
arm of the sea. 



and Tahoe are the highest large mountain lakes in the United States ; Crater 
Lake is the deepest lake in the United States ; Lake Baikal the deepest in the 
world. 



LAKES AND SWAMPS 



365 



The lakes in arid regions which have no outlet are generally either 
salt lakes or alkaline lakes. The salts carried in by the streams ac- 
cumulate in the lake, since the water is taken out by evaporation 
and the salts are left in the basin (Figs. 252 and 253). 

Playas are shallow depressions probably formed by wind blowing 
the dust away. After heavy rains the shallow basins are covered 
with water, forming a shallow lake. The water soon evaporates, 
leaving first a mud flat and then a dust plain, until the next rain. 
They are characteristic of deserts (Fig. 253). 




Fig. 253. — Mud cracks on playa lake plain in Nevada. (Photo by C. Van 

Duyne.) 



341. Swamps and Marshes. - — Swamps are for the most 
part closely associated with lakes and rivers, and are likewise 
a kind of connecting link between the water and land areas. 
There are both fresh-water and marine marshes. 1 The fresh- 
water swamps may be conveniently divided into river, lake, 
and upland swamps. 

The river swamps may be divided into terrace and flood- 

1 There is a tendency at present to use the word "swamp" for the fresh- 
water forms and "marshes" for the marine. 



366 



ELEMENTS OF PHYSICAL GEOGRAPHY 



plain swamps. The terrace swamps, sometimes called hillside 
bogs, are formed by the outcrop on the hillside of a bed of clay, 
shale, or similar rock that causes a continual seepage of the 
groundwater into the clay soil on the surface. They are 
abundant in the bituminous coal fields of the Appalachian 



1% 


C -dV 




B 






{ / 




%ms^ 


^^^^ 


/ ////. 


i 



Fig. 254. — Swamp and quaking bog formed by lake filling. D D, dia- 
tomaceous earth; / J, bog-iron ore; P P, peat; S, swamp; B, quaking bog; 
C, climbing bog. (After Shaler.) 

plateau, where they are caused by the outcrop of the clay 
bed's that underlie the coal seams. The flood-plain swamps are 
in great numbers on nearly every river flood plain and delta, 
as already described. (Figs. 204, 205.) 

Lacustrine or lake swamps are of two classes. The first class 
is formed on the lake margin, caused by a rise and overflow 




Fig. 255. — Climbing bog, C. (After Shaler.) 



of the lake, or by the elevation to the surface of all or part of 
the lake bottom through the accumulation of vegetable or 
animal remains, such as the shell deposits, which form the 
marl. The second class, known as quaking bogs, is caused in 
the final stages of lake-filling by vegetation, when the floating 
plants on the surface join those growing out from the shore, 
forming a continuous surface of vegetation across the remnant 



LAKES AND SWAMPS 



367 



of lake water underneath. The climbing bog, a sub-variety, 
is formed by the vegetation drawing the water by capillary 
attraction above the level of the lake, extending the bog 
above and beyond the former lake shore. (See Figs. 254 and 
255.) 

Upland swamps may be formed on clay soils by the accumu- 
lation of plant remains which prevent the rapid drying out of 




Fig. 256. 



View on Lake Drummond in Dismal Swamp, Va. (Photo by U. S. 
Geological Survey.) 



the moisture while the underlying clay retards its descent 
as groundwater. Such swamps sometimes build up many 
feet above the level of the surrounding flat on which they 
are located, and at times after heavy rains, have been 
known to burst and flood the adjoining areas with a mass 
of black mud or muck formed by the decaying vegetation 
(Fig. 256). 



368 



ELEMENTS OF PHYSICAL GEOGRAPHY. 



342. Salt Marshes. — Besides the fresh-water swamps there are 
vast areas of salt marshes along the seaboard. (See chapter on 
Shore Lines.) Professor Shaler estimated that there are at least 
350,000 acres of marsh land between New York City and Portland, 
Maine, and that 200,000 acres of this could be reclaimed, drained, 
and made into agricultural land that would have a value of 
$40,000,000. 




Fig. 257. 



Quarrying marl for Portland cement from swamp deposit near 
Jordan, N. Y. 



343. Economic Features of Swamps and Marshes. — Swamps and 
marshes are not entirely barren stretches. Among the many eco- 
nomic products from them might be named the following : rich 
agricultural land after drainage, timber, peat, cranberries, tripoli, 
marl, phosphates, bog-iron ore, game. They are also of great economic 
value in the regulation of streams. What other economic products or 
features of swamps can you name? Name some of the undesirable 
features of swamps. (Fig. 257.) 



LAKES AND SWAMPS 369 

QUESTIONS 

1. State the ways in which lakes decrease in size temporarily; 
permanently. 

2. Rivers are said to be the mortal enemies of lakes. Why ? 

3. How do rivers form lakes? 

4. Make a list of all the different kinds of lakes. 

5. Name the lakes in the United States the bottoms of the basins 
of which extend below sea level. Name two deep lakes that he far 
above sea level. 

6. Why are lakes formed by landslides generally short-lived ? 

7. Explain one way in which many small lakes or ponds are formed 
by man without building any dam above the surface. 

8. Make a list of all the lakes in the United States on which steam- 
boats run. 

9. How should you recognize a fossil lake? 

10. Make a list of all the different kinds of fishes and other animals 
that live in lakes. In another list name all those that live part of the 
time in the ocean and part in lakes or rivers. 

11. Why are many lakes used for summer resorts? 

12. On which side of Lake Michigan is vegetation less likely to be 
injured by frosts? On which side are the greatest peach orchards? 

13. How do swamps differ from lakes ? 

14. Many swamps occur on former lake areas. Would it be wrong 
to call swamps "children of the lakes"? 

15. What kind of swamps are not related to lakes ? 

16. Seneca Lake in New York is deeper than Great Salt Lake, but 
it is not as wide. Which one is likely to disappear first ? 

17. What kinds of lakes are characteristic of desert regions ? Name 
at least three kinds. 

18. How do swamps differ from marshes ? From bogs ? 

, 19. Explain how swamps may form on a nearly level plain and rise 
above the surrounding plain. 

20. Make a list of products obtained from swamps. 

21. Do swamps pay their way? That is, are their products more 
valuable than crops from equal areas of farm lands? 



CHAPTER XI 
CRUSTAL MOVEMENT AND VULCANISM 

So far our studies of the earth have been mostly about leveling 
agencies that disintegrate and wear down the uplands and carry 
the materials to the sea. Theie leveling agencies have been at 
work through all the past ages, and long ago they would have 
worn down all the land areas to or near the level of the sea if 
there had been no opposing forces to elevate them. 

In our previous studies we learned that the " everlasting 
hills " of the poets are being worn down and carried to the sea. 
We are now to learn how new hills, new land areas, are formed 
and old ones rejuvenated. After a first voyage on a stormy 
sea or a flying trip through the air it is a great relief to stand 
again on what we are pleased to call terra firma or the firm earth ; 
it seems to be so firm and solid. We are now to learn that 
terra firma is not always firm, but like other things it has its 
ups and downs. 

344. Evidences of Crustal Movement. — The surface of the 
earth is nearly everywhere being warped and twisted, sometimes 
up, sometimes down, and sometimes sideways. Occasionally 
the movements are sudden and produce earthquakes, but most 
frequently the movements are so slow as to be imperceptible 
to the casual observer. What is the evidence? How do we 
know that the surface of the earth is moving ; that it is sinking 
in some places and rising in others? 

(1) Some of the towns on the southern end of Sweden are 
slowly sinking and the sea is covering some of the streets, while 

370 



CRUSTAL MOVEMENT AND VULCANISM 



371 



the northern part of Norway is rising, and points that were on 
the shore a few centuries ago are now far above the highest tide. 
A Roman temple erected near Pozzuoli, Italy, in the third 
century slowly sank until the floor was twenty feet below the 
surface of the Mediterranean Sea, and later rose until it is again 
on the land above sea level. This depression and elevation 




Fig. 258. — Remains of Roman temple, near Naples, Italy. The temple 
was submerged nearly to the top of the large marble columns and then emerged 
to its present position without overthrowing the three columns. 



took place so quietly and slowly that three of the marble col- 
umns of the temple are still standing in their original position 
(Fig. 258). 

(2) Part of the old town of Port Royal on the Island of 
Jamaica may now be seen on the bottom of the bay. In 
Chapter X we learned that Reelsfoot Lake in Tennessee oc- 



372 



ELEMENTS OF PHYSICAL GEOGRAPHY 



cupies a depression on the Mississippi flood plain that sank 
in the year 1811. 

(3) In climbing the hills on the north side of Lake Superior 
one crosses several sand and cobble beaches marking old shore 
lines, the highest one more than three hundred feet above the 
present level of the lake. (See Fig. 259.) There are no cor- 
responding terraces on the south side of the lake. 

(4) Borings made in the bed of the Hudson River show river 
muds to the depth of several hundred feet overlying the old 




Fig. 259. Lake terraces, T T' T" T'", on the north shore of Lake Superior, 
showing successive elevations of the land north of the lake. The terraces formed 
by the waves mark temporary stops during the uplift. 



rock floor of the river. The land must have been hundreds of 
feet higher than at present when the old rock channel was cut 
by the river. Moreover, this former deep channel, not yet 
entirely filled with sediment, has been found to extend out on 
the continental shelf from the present mouth of the river. 
Since the river could not cut a channel on the sea bottom, this 
must have been a land area when the channel was formed. 

Many other examples might be cited in different parts of the 
world, indicating in some places uplift and other places sub- 
sidence of the earth's surface which have taken place in com- 



CRUST AL MOVEMENT AND VULCAN ISM 373 

paratively recent geologic time. Evidence of similar uplifts 
and depressions far back in geologic history is recorded in 
the rocks of the continents. (See Fig. 66.) 

The rocks in many places over the continents, on the plains, 
plateaus, and even on high mountains, contain multitudes of 
fossil remains of seashells, corals, and other animals that lived 
in the sea, showing that these rocks are made out of sediments 
laid down on a former sea bottom. The history written in 
the rocks tells us of the elevations and depressions in the past 
ages. (See Fig. 89.) 




Fig. 260. — Folded rocks. M , monocline ; S, syncline ; A, anticline. 

345. Causes of Crustal Movement. — A discussion of the cause 
or causes of the great warping of the earth's crust belongs in geology 
rather than geography. As students of geography we are concerned 
rather with the results of such movements as they affect the present 
surface features of the earth. In general it may be said that the 
primary cause or causes of the great crust movements are internal 
and the result directly or indirectly related to the heat of the earth's 
interior. 

346. Some of the Results of Crustal Movements. — The 

greatest results produced by crust movements on a large scale 
were the forming of the ocean basins and the continental areas. 
Secondary to these great movements were those causing uplifts 
of portions of the continental areas at different times into plains, 
plateaus, and mountains, as described in the following chapters. 
Since erosion is continuous on all land areas above sea level, 
it is evident that the height of any portion of a continent at 



374 



ELEMENTS OF PHYSICAL GEOGRAPHY 



any time is simply the excess of elevation over that of erosion 
and depression. When mountain areas are rising faster than 
they are being eroded, they are growing higher and larger ; 
when elevation ceases or is slower than erosion, then the moun- 
tains are growing smaller. 




Fig. 261. 



An anticlinal ridge in a water gap in the Allegheny Mountains in 
Maryland. (Photo by U. S. Geological Survey.) 



347. Folding and Faulting. — In the warping movement 
of the earth's crust the strata are in some places folded, 
crumpled, and broken, which produces a marked effect on the 
surface features, determining the shape and trend of the hills 
and valleys and resulting in a topography entirely unlike that 
of the eroded areas underlain by horizontal rocks. The fol- 



CRUST AL MOVEMENT AND VULCANISM 



375 



lowing terms are used to distinguish the different kinds or 
parts of folded rocks (Figs. 260, 261, and 262). 

The upward fold or crest of a rock wave is called an anticline; 
a downward fold corresponding to the trough of a wave is 
called a syncline; a simple downward or upward fold from one 
level to another is called a monocline. The line of direction 





191 >i 


• -•'i "BBS 


.,-.- 








V-' : - 






<> "41 


X' ' 






' "-3(H 


BBfiSc^ 


- 


snWi 


h % :> - v 




v . 


m\_ «fi& 


\ ' 1?%:' z 




^"^•"^ 


j 











Fig. 262. — A synclinal fold in a water gap in the Allegheny Mountains, near 
Hancock, Md. (Photo by U. S. Geological Survey.) 



along which the folding takes place, corresponding to the top 
of the anticline or the bottom of the syncline, is called the axis 
of the fold. A dome (or quaquaversal fold) is produced by- 
pressure underneath a point instead of a line, or it may be 
produced by horizontal pressure from all directions towards 
a point, resulting in an upward bulge resembling a dome. A 



376 



ELEMENTS OF PHYSICAL GEOGRAPHY 



reversed dome forms a basin. An elongated dome or basin 
is commonly called a canoe fold. Zigzag folds are produced 
by the bending or wrinkling of the axis of an anticline or syn- 
cline, causing the axis to take the shape of the letter S or Z. 

The most common types of folds are anticlines and synclines. 
They may be low, open folds, where the strata are slightly inclined 
to the horizontal, or compressed folds, where the strata are vertical 
or even overturned. The open folds are more common on plains 
and plateaus and the compressed folds in mountain areas. The 
effects of erosion on different kinds of folds is discussed in the follow- 
ing chapters on mountains and plateaus. 





c/- 


^Q£? 




/r- Z.-Z.- ------ 




/^=^=f^^Ei 




/ \ 1 " 




/ 1 LS 1 1 




1 1 1 


iX^r3^3^_- 


==y= 


^=-^^£^^^ 




"< ^ 


fe_ t- 


tt*± 


"p- 


^ ±s 




---------- 


y-V~--I-2-2 -is : 




I IT 

Fig. 263. — Cross section of faults : I, a normal fault ; II, a reverse fault. 



In the Allegheny Plateau region in western Pennsylvania and in 
West Virginia, the rocks are in places gently folded. Petroleum 
and natural gas occur along the axes of the anticlines, and coal beds 
occur in the synclines. The anthracite coal in eastern Pennsylvania 
also occurs in synclines. It has all been eroded from the axes of the 
intervening anticlines. 

348. Faults. — The movements of the earth's crust cause 
the rocks in some places to crack and break. The larger cracks 
are called fissures. Movement that causes displacement of 
the rocks along the plane of the crack or fissure produces a 
fault, and the plane of the fissure then becomes a fault plane. 
The fault plane may be vertical, horizontal, or any inclination 
between the two. It is more commonly nearer the vertical 



CRUSTAL MOVEMENT AND VULCANISM 



377 



than the horizontal. Where the fault plane is inclined to the 
vertical, the upper part, which hangs over the fault plane, is 
called the hanging wall. The opposite side, underneath the 
fault plane, is called the foot wall. A downward movement 
of the hanging wall with reference to the foot wall produces 





•^torf 1 






'* 


B 
;"v> 




^^~ *Bk ■ -/***!•'' .■■■■ 


s *i 


■" 4^»c**5 ■■:■ 






BBEeS^j^^'-^^'-^ -^^i^S 


U5 ; . ;•% 


' ^- r ... i .•> , ' 




j5]§yjfSSfc"'' • v.,' ■? 


T-.* K' * X " ■ V *■>. - 


8&*- -V"**-' 
■■>■ up N 


. T. * / ^ ' 


. i«T V-*l.?- 



Fig. 264. — A reverse fault near Jamesville, N. Y. Fault plane extends 
from near the upper right corner to near the lower left corner. (Photo by the 
author.) 



a normal or gravity fault; the opposite movement produces 
a reverse or thrust fault. (See Figs. 263 and 264.) 

The exposure of the fault plane above the surface of the earth is 
called a fault scarp, and forms the side of a hill or mountain, depend- 
ing upon the extent of the movement, whereas the steepness of the slope 
depends, upon the inclination of the fault plane to the vertical. 
Weathering and erosion soon destroy the regularity of a fault scarp, 



378 



ELEMENTS OF PHYSICAL GEOGRAPHY 



and when carved by gullies and covered with mantle rock it is difficult 
to recognize its relation to a fault. The slopes of many of the 
mountains in the Great Basin region in Utah and Nevada and the 
slopes of the Wasatch Mountains, east of Great Salt Lake, are 
weathered fault scarps (Fig. 265). 

The eastern face of the Rocky Mountains for many miles north 
of the Glacier Park Hotel in Glacier National Park is caused by an 




Fig. 265. — Fault scarp formed during the San Francisco earthquake in 1906. 
The scarp was formed by the foreground dropping down seven feet. (Photo by 
J. C. Branner.) 



enormous nearly horizontal thrust fault which has caused these rocks 
to be pushed for some miles eastward out on the plain. The present 
mountain slope is on the weathered edges of the rocks forming the 
hanging wall of the fault. The fault plane may be seen in some of 
the deep valleys that have been cut down through these rocks into 
the newer rocks of the underlying foot wall. 

349. Horizontal Faults. — ■ Faults produced by horizontal move- 
ments, instead of vertical movements of the rocks, are known as hori- 



CRUST AL MOVEMENT AND VULCAN ISM 



379 



zontal faults. If the horizontal fault plane corresponds to a bedding 
plane in the sedimentary rocks, it does not affect the topography. 
If the movement is along a vertical or inclined plane, it does not appear 
different from a fissure or a crack on a level surface, but where the 
fault plane crosses a ridge or valley, there is an offset or notch on the 
hillsides. 




Fig. 266. — Remains of a fissure formed by the earthquake of 1811 on the flood 
plain of Mississippi River in Missouri. (Photo by M. L. Fuller.) 

350. Earthquakes. — An earthquake is a tremor or shaking 
of the earth from natural causes. The sudden movement of 
large rock masses along a fault plane is one of the most common 
causes of earthquakes. 

The great earthquake in California on April 18th, 1906, 
accompanied a movement of rocks along a fault plane extend- 
ing from Mt. Pinos on the south to Point Arenas on the north, 
a distance of 375 miles. It is a fault of the horizontal type 
on a nearly vertical plane, in which the lateral movement of 



380 ELEMENTS OF PHYSICAL GEOGRAPHY 

these rocks on the two sides of the fault plane varied from six 
to twenty feet. The movement was on a pre-existing fissure, 
along which movements had taken place at various times in 
ages past. In 1872 the village of Lone Pine in eastern Cali- 
fornia was destroyed by an earthquake accompanying the 
movement of the rocks along a fissure 200 miles long. These 
are only two of a number of fault planes in the mountainous 
region of California, on some of which slight movements have 
taken place in recent years, while some of them show no evi- 
dence of movement in historic times. 

During a series of earthquake disturbances in the Mississippi 
Valley, beginning in 1811 and continuing for several months, 
a number of fissures and faults were formed on the flood plain 
of the Mississippi between St. Louis and Memphis. Most 
of these cracks have been obliterated by erosion or covered 
by river sediments, but some of them have not yet been com- 
pletely destroyed (Fig. 266). 

Other causes which, produce earthquakes are volcanic eruptions, 
landslides, falling of large masses of rocks from the roofs of caves, 
slumping of large masses of material from the edge of the continental 
shelf or possibly from the end of a delta. The eruption of Krakatoa 
in the East Indies in 1883 produced an earthquake that shook the 
entire globe. Great landslides such as that at Frank, Alberta, pro- 
duce slight earthquakes. 

Earthquakes are among the most impressive manifestations of the 
giant forces of nature. The suddenness with which great numbers 
of lives are lost and vast amounts of property destroyed makes an 
indelible impression on the human mind. But as a factor in changing 
the physical geography of the earth it is surpassed by many of the less 
spectacular forces. Most of the changes produced by an earthquake 
are local and soon obliterated. It requires a careful observer to find 
any existing evidences of the great earthquake that frightened so 
many people in the Mississippi Valley in 181 1-1812, or of the earthquake 
that destroyed so much property in Charleston in 1886. In a few 
years more most of the marks of the great earthquake of 1906 in 
California will be obscured. 



CRUSTAL MOVEMENT AND VULCANISM 381 

351. Great Changes Produced Slowly. — The forces that 
produce the great changes in the physiography of the earth 
are those that are acting through long periods of time, and 
so slowly that their existence is scarcely recognized by the 
casual observer, such for example as the interior forces that 
elevate great mountain ranges and plateaus, and the opposing 
forces that cut the canyons and carve out the great valleys 
and finally wear down the mountains and plateaus. How 
many of the readers of this book have seen any physical features 
produced by earthquakes? But no one can open his eyes out 
of doors without seeing in every landscape the results of the 
quiet giant forces discussed in the preceding chapters; even 
the earthworms and the ants have produced greater changes 
on the earth than the earthquakes. 

VITLCANISM 

352. Volcanic Action. — Besides the warping movements 
discussed in the preceding pages, which produce elevations 
and depressions of the earth's surface, elevations large and 
small are built up on the surface from material extruded from 
the interior through openings in the rocks of the earth's crust. 
Vast quantities of molten rock are also intruded into the bed 
rocks without reaching the surface. 

All the phenomena associated with intrusion and extrusion 
of the heated materials into or through the earth's crust are 
included under vulcanism, one important phase of which is 
the volcano. 

353. Volcanoes. - — A volcano is a somewhat circular or pipe- 
like opening in the earth's crust, through which heated materials 
from the interior pour out or are thrown out on the surface. 
Much of the material is deposited near the opening, building up 
mounds, hills, or mountains. The more or less funnel-shaped 
opening at the top is called a crater (Figs. 132 and 267). 



382 



ELEMENTS OF PHYSICAL GEOGRAPHY 



354. Active, Dormant, and Extinct Volcanoes. — Some 
volcanoes are active for a few months or years, and then 
activity ceases, it may be for a few months or years or per- 
manently. Volcanoes which erupt at more or less frequent 
intervals are said to be active, those which have been quiet 
for a long period are called dormant, and others are thought to 
be extinct (Fig. 268). 




Fig. 267. 



Mt. Shasta, Calif. An extinct volcano on the Cascade Moun- 
tains. (Photo copyrighted by C. R. Miller.) 



355. Active Volcanoes. — There are about 300 volcanoes 
that are active or have been active in recent years. How 
many of the supposed dormant and extinct volcanoes may 
become active is not known. The numerous volcanoes on the 
Cascade Mountains in western United States were thought to 
be extinct, but a few years ago Lassen Peak in northern Cali- 
fornia began erupting and is still in activity (1918). 

356. Mt. Vesuvius. — At the beginning of the Christian 
era Mt. Vesuvius was supposed to be extinct, but in the year 
79 it became violently active, destroying the cities of Pompeii 



CRUSTAL MOVEMENT AND VULCANISM 383 

and Herculaneum. It has been intermittently active ever 
since, although there was one period of quiescence of nearly 
500 years. As recently as 1906 there was a great erup- 
tion in which vast quantities of material were thrown out 
and great streams of lava poured down the mountain side, 
destroying much property and killing many people. (See 
Fig. 132.) 




Fig. 268. — Mt. Pelee, an active volcano in Maitinique. August 30, 1902. 
(Photo by American Museum of Natural History.) 

357. Krakatoa. — The most violent volcanic eruption in modern 
times was on the island of Krakatoa in the East Indies in 1883. The 
noise of this eruption was heard nearly 3000 miles, probably the 
loudest noise there has been on the earth since it was inhabited by 
man. Two-thirds of the island was blown into the air, some of it 
to a height of 17 miles, part of it such fine dust that it was three years 
or more before all settled out of the atmosphere. Where part of the 
island stood before the eruption the ocean was 1000 feet deep after- 
wards. 



384 



ELEMENTS OF PHYSICAL GEOGRAPHY 



358. Volcanic Materials. — The materials ejected from 
volcanoes consist of : (1) gases and vapors, (2) solid ma- 
terials, (3) liquid material or molten lava. 

The gases consist of water vapor, carbon dioxide, carbon 
monoxide, sulphur, chlorine, arsenic, mercury, etc. They 
frequently carry great clouds of dust which appear like smoke. 




Fig. 269. — Volcanic fragments ejected from Mt. Pelee, August 30, 1902, 
now lying on the plateau about one mile from the crater. (Photo by American 
Museum of Natural History.) 



The solid material consists partly of rock fragments and 
dust torn from the solid rocks by the force of the explosion 
and partly of the molten rock that is blown from the molten 
mass and cools in the air, falling to the earth in solid fragments 
(Fig. 269). 

The finest material settles as volcanic dust, which when 



CRUST AL MOVEMENT AND VULCAN ISM 385 

partially hardened forms volcanic tufa or tuff; the coarser 
fragments of lava that have cooled in the air are called lapilli 
or cinders; still larger masses are called volcanic bombs (Figs. 
270 and 271). 

Lava is the molten rock that pours out in streams or sheets, 
sometimes from the crater, but frequently through cracks or 




Fig. 270. — Volcanic tufa, composed of consolidated volcanic dust from Mt. 
Vesuvius. Now being quarried for building stone in Naples. (Photo by the 
author.) 

fissures in the side of the cone. Lava when cooled forms 
obsidian, vesicular lava, pumice, basalt, etc. (Fig. 272). 

359. Volcanic Cones. — Some volcanic cones have very 
steep slopes, some gentle slopes, and some a broad, nearly flat 
base and a steep cone at the top. If the volcano is one of the 
explosive type, in which the materials are blown into the air 
and fall down around the crater, it builds up a steep " ash 
cone," such as Mt. Nuovo near Naples. If the eruption is 



386 ELEMENTS OF PHYSICAL GEOGRAPHY 

of the quiet type, in which the lava wells up and overflows, 
the lava streams flow long distances and form a very much 
flattened cone, like those of the Hawaiian volcanoes. Some 
volcanic mountains are of the mixed type, that is, a mix- 
ture of ash deposits and lava flows, such as Mt. Vesuvius. 
(Fig. 273.) 




Fig. 271. — Volcanic bomb and lava fragments on volcanic plateau in Idaho. 
(Photo by U. S. Geological Survey.) 

Sometimes as activity ceases in a volcano the lava sinks down into 
the earth, and the top of the mountain sinks down and is absorbed in the 
lava, producing a large crater some miles in diameter. In some 
instances a violent explosion in a volcano that has been dormant 
for some time blows away the top of the mountain, producing a large 
crater. The large craters produced by the sinking of the mountain 
top or by blowing away the top of the mountain, are called calderas. 
Crater Lake in Crater Lake National Park in the Cascades occurs 
in a caldera formed by the sinking down of the top of old Mt. 
Mazama. 



CRUSTAL MOVEMENT AND VULCANISM 387 




Fig. 



272. — Dissected lava flood showing basaltic columns at Basalt 
Cliff, Wash. (Photo by U. S. Geological Survey.) 



388 ELEMENTS OF PHYSICAL GEOGRAPHY 

360. Distribution of Volcanoes. — There are a great number 
of volcanoes located around the border of the Pacific Ocean. 
Beginning at the extreme southern end of South America, they 
occur at intervals on the mountain range through South 
America, Central America, the United States, and Alaska, 
following the Aleutian Islands across to Asia and down the 
Asiatic coast. This chain contains some of the largest and 




Fig. 273. — A driblet or cinder cone, built up by a vent in lava stream, near 
Flagstaff, Ariz. (Photo by U. S. Geological Survey.) 

most active volcanoes of the world, as well as many dormant 
and extinct ones. There are several groups of volcanoes in 
the Pacific Ocean, the best known of which are probably 
Kilauea and Mauna Loa in the Hawaiian Islands. There 
are some in the Atlantic Ocean, on Iceland, and in the West 
Indies, a number in and near the Mediterranean Sea, and some 
on Antarctica near the South Pole. They occur also in Central 
Europe, in Asia, in Africa, and in the interior of North America. 



CRUSTAL MOVEMENT AND VULCANISM 



389 



They are thus pretty well scattered in all latitudes over the 
globe on both the ocean and the continental areas. 

There are probably many volcanic peaks scattered over the bottom 
of the deep seas, the existence of which is not known, because their 
tops do not extend above the level of the sea. 

361. Volcanic Intrusions. — The intrusive forms of vulcan- 
ism, that is, the molten rocks that penetrate the earth's crust 
but do not extend to the surface, are frequently exposed at 




Fig. 274. 



Outcrop of volcanic dike on slope of Spanish Peaks, southern 
Colorado. (Photo by B. W. Clark.) 



the surface by subsequent erosion of the overlying rocks 
and produce distinctive topographic forms. 

Dikes, the most common form of intrusions, are formed by 
molten rock rising in and filling cracks in the earth's crust. 
In some cases the molten rock rises through the fissure to the 
surface and spreads out as a sheet of lava, which obscures the 
dike until the overlying sheet is eroded. Sometimes the dike 
terminates in the rocks below the surface and its existence is 
not known until the overlying rocks are eroded. In either 



390 ELEMENTS OF PHYSICAL GEOGRAPHY 

case, after the overlying rocks are removed, further erosion 
brings the dike into prominence : if the dike is more resistant 
than the bordering rock, it is left projecting above the surface 
like a wall ; if it is less resistant, it wears away more rapidly 
and forms a depression on the surface. (Fig. 274.) 

Laccolites are intrusions through a pipe-like opening to near 
the surface, where they bulge up the overlying rocks into a 
dome shape. After erosion of the surface rocks, the igneous 
rocks of the laccolite are exposed in a more or less dome-shaped 
hill or mountain. (See Fig. 304.) 

Stocks are more or less conical intrusions of igneous rocks, generally 
larger than dikes or laccolites, and consisting of granitoid rocks. 

QUESTIONS 

1. Cite all the evidence you can that portions of the earth's surface 
have been elevated ; that other portions have been depressed. 

2. Illustrate by diagrams the different kinds of folds. 

3. Explain the distinction between a fissure and a fault ; between 
a normal and a reverse fault. 

4. Give the names and dates of all the destructive earthquakes of 
the United States. Would the explosion of a powder magazine cause 
an earthquake? 

5. Name some forces that produce greater changes on the earth 
than earthquakes. 

6. What is a volcano? 

7. How does a new volcano differ from one that has been active a 
long time? 

8. How does a volcano recently extinct differ from one that has 
not been active for many centuries ? 

9. Make a list of all the different kinds of material thrown out of 
volcanoes. 



CHAPTER XII 
PLAINS AND PLATEAUS 

The larger physiographic features of the land areas are clas- 
sified as plains, plateaus, and mountains. Many kinds and 
varieties of each of these, based on differences in size, origin, 
and surface details, give complexity and variety to the ever- 
changing landscape as one travels over the land areas. The 
surface of the plains has less variety, fewer of the bold and 
picturesque features that characterize plateaus and mountains, 
but they are more easily cultivated, have richer soils, are more 
easily traversed, and hence capable of supporting a greater 
population than the upland areas. The plains supply a large 
part of the food of the world. 

Plains are areas of low relief with comparatively even sur- 
faces. Generally they occur at lower levels, that is, nearer 
sea level than plateaus, although there are some exceptions 
to this. 

PLAINS 

362. Kinds of Plains. — Plains are formed (1) by ag- 
gradation, (2) by elevation, (3) by aggradation and elevation, 
(4) by degradation or erosion, (5) by erosion and depression, 
or by a combination of these processes. They disappear by 
elevation into plateaus or mountains, or by depression and 
submergence into submarine plains. Since elevation and 
depression take place in a number of different ways, and since 

391 



392 ELEMENTS OF PHYSICAL GEOGRAPHY 

there are different kinds of eroding and depositing agents, 
there are many different kinds of plains in various stages of 
construction or destruction. 

363. Coastal Plains. — Coastal plains are uplifted portions 
of the marginal continental shelf which have been added to the 
former land areas as the shore line receded seaward. They are 




Fig. 275. — View on the Atlantic Coastal Plain. Cypress trees and knees in 
Dismal Swamp, Va. (Photo by U. S. Geological Survey.) 

portions of the submarine plain that have been added to the 
land areas by elevation. A coastal plain is narrow or wide, 
depending on the width and depth of the submarine plain and 
the extent of the uplift. 

On the Pacific Coast of the United States there is a narrow 
strip of coastal plain on the southern California Coast and a 
few small patches farther north. The coastal plain of the 



PLAINS AND PLATEAUS 



393 



Pacific Coast is small because the continental shelf along 
the Pacific Coast is narrow and slopes rapidly into the deep Pa- 
cific Ocean, and the Coast Mountains he close to the shore, in 
fact project into the ocean in places. 

On the Atlantic Coast there is no coastal plain north of Cape 
Cod because that portion of the coast has been depressed to 
such an extent that the sea laps up on the old land area. There 
is a narrow strip of coastal plain on Cape Cod and Long Island. 




Fig. 276. — Section showing the dip of the beds in the Atlantic Coastal Plain- 
towards the ocean, which is to the right of the view. (Photo by Maryland 
Geological Survey.) 

From New York southward it widens to nearly two hundred 
miles on the south Atlantic Coast (Fig. 275). 

On the Gulf Coast there is a broad strip of coastal plain that 
narrows somewhat at the western end next to the Mexican 
border. It is bisected by the Mississippi flood plain and 
delta, which forms a broad strip of alluvial plain between the 
eastern and western portions. 

The rocks of coastal plains consist of sediments, such as 
gravel, sand, silt, clay, marl, and chalk, deposited in the former 
shallow sea that covered the area. Interspersed in the marine 



394 



ELEMENTS OF PHYSICAL GEOGRAPHY 



sediments in places are some flood-plain and delta sands and 
silts and some lignites composed of accumulated vegetation 
that have been buried under the other sediments. In places 
the sediments have been indurated into sandstones and shales, in 




Fig. 277. — Banded coastal plain. Outcrops of different layers form bands 
nearly parallel with the shore. Edges of the harder layers form low hills or 
cuestas. 



other places they are slightly hardened, but in many places they 
are little harder than when they were first laid down (Fig. 276). 

Since the uplift was usually greatest on the land side, the beds 
generally dip towards the sea and in fact extend out under the sea 
beneath the sediments that are now forming. The structural con- 



PLAINS AND PLATEAUS 395 

ditions are thus favorable for artesian wells, as the coarse sands and 
gravels carry more water than the beds of fine mud and clay which 
hold the water under pressure. A large part of the water supply for 
the borough of Brooklyn is obtained from artesian wells on the coastal 
plain of Long Island (Fig. 276). 

The soils formed on the outcropping edges of the coastal-plain rocks 
extend in more or less well-defined soil belts or bands, in general 
parallel with the shore. Greater erosion on the edges of the weaker 
beds leaves the harder ones standing up as low ridges separated by 
broad valleys or depressions eroded on the softer beds. (See Fig. 277.) 

An embayed coastal plain is one which, after elevation and 
erosion, has been depressed, causing the shore line to advance 
again on the land. The sea extends up the river valleys, form- 
ing bays and estuaries, thus drowning the lower valleys and 
dismembering the streams. The Atlantic Coastal Plain is 
an example. The Chesapeake Bay is the drowned portion 
of the Susquehanna River. The James, Potomac, and other 
rivers, which were formerly tributaries of the Susquehanna 
River, have been dismembered and now flow into the bay. 
Delaware Bay is the drowned portion of the Delaware River. 
The Hudson River was drowned at the same time and forms 
an estuary extending beyond the coastal plain, far back into 
the old rocks of the continent. North from New York the 
entire coastal plain has been submerged, except the small 
fragments left on Long Island and Cape Cod. (Fig. 278.) 

364. Alluvial Plains. — Alluvial plains are river flood plains 
described in Sees. 259, 260, and 280. The largest one in 
the United States is that of the lower Mississippi River, which 
covers an area of many thousand square miles. There are large 
alluvial plains along the Sacramento and San Joaquin rivers 
in California, and smaller ones on portions of nearly all the 
rivers in the United States. The Hudson and Niagara rivers 
have no flood plain. On many of the streams flowing through 
mountains or plateaus, the alluvial plains are generally narrow 
strips, sometimes found only on one side of the river. On the 



396 Elements of physical geography 




Fig. 278. — Pine forest on the coastal plain in Georgia. 
Bureau of Forestry.) 



(Photo by U. S. 



smaller streams the alluvial plains are commonly called " bottom 
lands," " river bottoms/' or " creek bottoms." 

The deltas of the larger rivers are covered with alluvial soil 
similar to that on the flood plain, in fact, it is simply the ex- 
tension of the flood plain over the land newly reclaimed by the 



PLAINS AND PLATEAUS 



397 



delta. The delta plains are near sea level and the outer margins 
are frequently fringed with salt marshes. Lakes, lagoons, and 
swamps are common surface features. The largest delta plain 
in the United States is that of the Mississippi, which covers a 
large part of southern and southeastern Louisiana. The delta 
of the Colorado River in southern California and adjoining 





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Fig. 279. — Scene in a cotton field on the Mississippi Alluvial Plain, 
by U. S. Department of Agriculture.) 



(Photo 



portions of Mexico extended across the Gulf of California, 
separating the Salton Basin from the gulf. The Colorado 
River has practically no flood plain along the greater part of 
its course, but its delta is next to that of the Mississippi in size 
among the deltas of the United States. 

365. Use of Alluvial Plains. — The greater part of all al- 



398 



ELEMENTS OF PHYSICAL GEOGRAPHY 



luvial plains, both flood plains and deltas, is covered with a 
rich deep soil well adapted to agriculture. They are generally 
the first lands to be brought under cultivation in the settle- 
ment of a new country, and they retain their fertility longer 
than almost any other class of soils. The flood plain and delta 
of the Nile and the Hoangho of China are among the oldest 



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wf T" IT ~ M " T*"~ * ' f *" Wm 1 


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Fig. 280. 



Transporting cotton bales by steamboat on the Mississippi River. 
(Photo by U. S. Department of Agriculture.) 



continuously settled areas in the world. They have furnished 
the food supply for a dense population for many, many centuries. 
Both of these areas are among the most densely populated in 
the world. (Figs'. 279 and 280.) 

The reasons for the productiveness of the alluvial plains 
are : (1) the soils are the finer, richer portions washed from the 



PLAINS AND PLATEAUS 



399 



slopes of the upper valleys ; (2) the fertility is renewed from 
time to time by the overflows which deposit new layers ; (3) the 
water table lies so near the surface that the areas suffer from 
drouth less than do the uplands. The productivity is enhanced 
by the fact that (4) communication and transportation by 
road, railway, and river are easy except during the flood season. 




Fig. 281. 



Sugar cane on the alluvial plain of the Mississippi River, 
by U. S. Bureau of Agriculture.) 



(Photo 



The greatest drawbacks to prosperity on the alluvial plains 
are : (1) destruction of life and property from the floods ; and 
(2) malarial conditions from the many mosquitoes that breed 
in the stagnant water. 

The alluvial plain of the lower Mississippi has produced large 
crops of cotton, sugar, rice, and other products since the ter- 
ritory was first settled (Fig. 281). The bottom lands of the 
tributaries in the central Mississippi Basin are famed for their 
big corn crops The delta of the Colorado River was unsettled 



400 



ELEMENTS OF PHYSICAL GEOGRAPHY 



for a long time because of the dry climate, but now that the 
water of the river has been led out through irrigation ditches, 
this delta is proving, like all deltas, the richness of its alluvial 
soil. In addition -to the rich soil, the warm subtropical tem- 
perature on the Colorado delta adds to the productiveness by 
giving a continuous growing season. 




Fig. 282. 



View on the alluvial plain of John Day River, 
U. S. Bureau of Agriculture.) 



Ore. (Photo by 



The large alluvial plains of the Sacramento and San Joaquin 
Rivers are very productive farming regions, owing to the warm climate 
and long growing season, combined with the rich soil. They pro- 
duce bountiful crops of barley, wheat, rice, and other grains, sugar 
beets, and fruits of different kinds, besides large numbers of domestic 
animals (Pigs. 137 and 282). 

The flood plain and delta of the Nile River in Egypt and of the 
Yang-tse-kiang and Hoangho of China support large cities as well as 
many smaller cities and villages. Very few of the large cities of the 



PLAINS AND PLATEAUS 



401 



United States are on alluvial plains. The largest cities in this country 
are centers of manufacturing and commerce, industries which favor 
concentration in large cities. The agricultural industry of alluvial 
plains is better served by more widely distributed smaller cities and 
villages. Because the uplands are more healthful and pleasant places of 
residence, the bottom lands along many of the smaller rivers and creeks 
are cultivated by farmers who live on the river bluffs. (Fig. 233.) 

366. Colluvial Plains. — Bordering many of the mountains of the 
west and southwest, there are more or less extensive plains covered 




Fig. 283. — Alluvial plain at head of Chesapeake Bay, Md. 
Maryland Geological Survey.) 



(Photo by 



with materials carried from the mountain slopes partly by gravity 
and partly by rainwash that did not follow Well-defined stream chan- 
nels. Part of it was possibly carried in temporary gullies or "washes," 
but much of it was by sheet erosion, in which a sheet of water covered 
the greater part of the slope, sweeping the material with it out on the 
bordering plain. Such deposits are called colluvial, and the resulting 
plain a colluvial plain. 

367. Lacustrine Plains. — A lacustrine plain is one that was 
formerly covered with lake water. It may represent the entire 
area of a former lake or a portion of it. A lake plain may be 



402 ELEMENTS OF PHYSICAL GEOGRAPHY 

formed by (1) the filling of a lake basin, (2) the evaporation 
of the water due to a change in climate, or (3) the draining of 
a lake or part of it by the cutting down of the outlet or the 
tilting of the lake basin. 

Over the northern United States, from the Rocky Mountains 
to the Atlantic Coast, there are hundreds of small lacustrine 
plains formed by the filling of shallow water basins left by the 
continental glacier. The final filling of these basins was by 
muck and marl, leaving the surface covered with a black 
organic soil of great richness. Much of these lacustrine black 
lands are now used in growing celery, onions, and other vege- 
tables for the city markets. 

A large part of the great wheat district of North Dakota 
and Manitoba is on the lacustrine plain of a former great lake, 
called Lake Agassiz. Great Salt Lake is but the remnant of 
a former large lake, Bonneville, and the rich farm lands north 
and south of Salt Lake City are on the bed of old Lake Bonne- 
ville. Strips of lacustrine plains border the south side of Lakes 
Ontario, Erie, and Michigan, and surround Lake Tulare in 
California and the lakes of southeastern Oregon. (Fig. 284.) 

In places along the old shore lines of some of these former lakes 
there are great sand and gravel terraces, the materials of which are 
utilized in building operations in near-by cities. The city of Syracuse, 
New York, is built on a lacustrine plain, and the sand and gravel used 
in construction work in the city is obtained from the old beach of the 
now extinct Lake Iroquois. 

368. Glacial Plains. — A continental glacier, such as that 
which covered northern United States, leaves many plains 
large and small on the area which it covered. The glacial 
plains are formed in part by the degrading action of the glacier 
in wearing down the elevations, and in part by aggrading action 
in filling up depressions. 

While glaciers deposit materials on both uplands and low- 
lands, in general more material is deposited in the valleys than 



PLAINS AND PLATEAUS 403 

on the hills. Gullies and small valleys across which the ice 
moved, were frequently filled entirely or in part by moraines 
left by the ice. The advancing glacier widened and deepened 
some of the valleys extending in the direction of the moving 
ice, but as the ice melted away, the moraine in the ice was 
left in the bottom of the valley along with the materials washed 
in from the bordering hills. 




Fig. 284. — Flax on lacustrine plain in North Dakota. (Photo by U. S. 
Department of Agriculture.) 

Many of the plains in the glaciated region were no doubt plains 
before the coming of the glacier. In limited areas the surface has 
probably been made more irregular than it was before, owing to the 
drumlins, kames, eskers, and recessional moraines. But the glacier 
wore away more elevations than it built up and filled more valleys 
than it made, leaving the surface with more and larger plains than it 
had before. Many of the lacustrine plains mentioned in the preceding 
section lie on glacial plains, and were caused indirectly by the glacier 
(Fig. 284). 



404 ELEMENTS OF PHYSICAL GEOGRAPHY 

369. Peneplains. — In Chapter VIII we learned that all 
land areas subject to long continued erosion are finally worn 
down in their old age to a plain which in its later stages is 
called a peneplain (almost a plain) . It is a plain of degradation 
from which the overlying material has been worn away, instead 
of an area upon which new materials have been laid down. It 
furnishes the material which, laid down elsewhere, forms an 




Fig. 285. — Orange groves on peneplain in southern California. Monad- 
nocks in background. (Photo by U. S. Department of Agriculture.) 

alluvial, marine, or lacustrine plain, but after this material has 
all been worn away, the area from which it was carried becomes 
a plain of erosion. A large peneplain contains alluvial, lacus- 
trine, and other kinds of smaller plains. 

The surface of a peneplain is rarely as even or regular in its 
surface as the built up plains, as indicated in its name. There 
are hills or even mountains, called monadnocks, scattered over 
the surface. The final stage of a peneplain is the base-leveled 



PLAINS AND PLATEAUS 



405 



plain, but the erosion of the last elevations is so slow that it 
rarely reaches base level before it is either elevated and dis- 
sected by the rejuvenation of the streams, or is submerged 
and covered with new deposits. (See Fig. 201.) 

Southern California, between Riverside and Los Angeles, 
is a peneplain. The north part of it, between San Bernardino 




Fig. 286. — Peneplain in Shenandoah Valley, near Natural Bridge, 
Monadnocks in background. (Photo by U. S. Geological Survey.) 



Va. 



and Pasadena, is covered with the piedmont alluvial fan 
composed of materials washed out of the San Bernardino 
Mountains (Fig. 285). 

New England was at one time a peneplain, but it has been elevated 
and eroded so that the uplands between the many valleys are all that 
is left of the original plain. 

The- piedmont region between New York City and northern Georgia 
was at one time a peneplain, which has been uplifted and tilted 



406 



ELEMENTS OF PHYSICAL GEOGRAPHY 



towards the ocean, and its eastern part submerged and covered by 
the coastal plain. The western part, which was uplifted, has been 
dissected by the revived streams. The Allegheny Mountains have 
been carved by erosion out of an uplifted peneplain, and the tops 
of the mountains are all that are left of the original plain (Fig. 
286). 

(For description and explanation of the uplifted and dissected 
peneplains of the eastern United States consult the following National 




Fig. 287. — View on an alkali plain, Malheur Basin, Ore. (Photo by U. S. 
Geological Survey.) 



Geographic monographs : (1) The New England Plateau, by Davis, 
(2) The Northern Appalachians, by Willis, and (3) The Southern 
Appalachians, by Hayes.) 

370. Salt and Alkali Plains. — Many of the plains in arid 
regions are covered in part with deposits of salt or alkali, or 
a mixture of the two. They occur only in dry regions, where' 
the evaporation is greater than the precipitation. In humid 
regions the soluble salts are carried to the sea in the run-off 



PLAINS AND PLATEAUS 



407 



waters, but in arid regions there is no run-off, so the soluble 
salts leached from the rocks accumulate on the plains where 
the waters evaporate. In the United States, salt and alkali 
plains occur in the Great Basin region west of the Rocky 
Mountains in Utah, Nevada, California, and Arizona. They 
also occur in southeastern Oregon, on the western border of 




Fig. 288. 



Cornfield on the prairie plains in the Mississippi Basin, 
by U. S. Department of Agriculture.) 



(Photo 



the Great Plains east of the Rocky Mountains, and in New 
Mexico and western Texas (Fig. 287). 

371. Tundras. — Tundras are the frozen plains of the far north 
in North America, Europe, and Asia. In these areas the ground is 
perpetually frozen to a depth of a hundred feet or more. During 
the short summer season the surface thaws to the depth of a few feet 
and is covered with a dense growth of mosses and other plants, but the 
growing season is too short to support tree growth. 



408 



ELEMENTS OF PHYSICAL GEOGRAPHY 



372. Prairie Plains. — Through the central and north 
central Mississippi Basin are great stretches of treeless plains, 
called prairies, which in the virgin state were covered with a 
luxuriant growth of grass and wild flowers, but no trees. They 
are now nearly all under cultivation and produce large crops 
of corn, wheat, and other products, and are now dotted with 
groves of trees that have been planted there by man. 





Fig. 289. 



View on the Great Western Plains. Bunch grass of the grazing 
area. (Photo by U. S. Geological Survey.) 



The larger prairies of Illinois, Iowa and Minnesota, Kansas 
and Nebraska, and the smaller prairies of Wisconsin, Indiana, 
and Ohio are all in the region covered by the continental glacier, 
but there are similar prairies in Oklahoma and Texas, south of 
the glaciated area. The prairies are covered with a deep, 
rich soil that proves very productive under cultivation (Fig. 
288). 



PLAINS AND PLATEAUS 409 

Similar treeless plains in Russia are called steppes, in South. America 
they are called pampas and llanos. Small treeless grass-covered 
plains on the south Atlantic Coastal Plain are called savannas. In 
the Adirondack Mountain region in New York small treeless plains 
are called vlies. 

373. The Western Plains. — The Great Western Plains of 
western Kansas and Nebraska, eastern Montana and Wyoming, 
eastern Colorado, and western Texas are treeless plains, but 
not prairies, although they are sometimes called so. The 
western plains do not grow the tall, luxuriant grass of the 
prairies, and are not covered with the dense meadow-like sod 
of the prairies. Covered with the short buffalo or bunch grass, 
which grows in scattered tufts, they are unlike the grassy 
meadows of the prairies. The bunch grass, though short and 
scattered, is very nutritious and makes excellent grazing. 
In the wild state it supported vast herds of bison, antelopes, 
and other animals, and now supports great herds of cattle, 
horses, and sheep (Fig. 289). 

PLATEAUS 

374. Plateaus. — Plateaus resemble plains in having broad 
stretches of comparatively even surface. They are unlike 
plains in that the streams draining the area flow in deep, narrow 
valleys or canyons, in which they resemble mountains. 
Plateaus are generally bordered on one or more sides by lower 
land, in which they resemble mountains, but they differ from 
mountains in that they have broad, comparatively even tops, 
while mountains have narrow, rugged tops. Plains are bor- 
dered by higher land, mountains, or plateaus, or as in some 
instances, as in coastal plains, in part by water ; plateaus are 
bordered in part at least by lower land, usually plains. Gen- 
erally plateaus are higher than plains, but there are some 
exceptions. 

The Appalachian Plateau was at one time a plain. It was 



410 



ELEMENTS OF PHYSICAL GEOGRAPHY 



elevated, and the streams cut deep canyons into the surface, 
and thus it became a plateau. In some places the canyons 
have become so numerous that the upland has been dissected 
into fragments with narrow tops, and such portions are called 




Fig. 290. 



Entrenched river valley in the Allegheny Plateau, W. Va. 
by U. S. Geological Survey.) 



(Photo 



mountains. The Catskill Mountains, the mountains of West 
Virginia, and the Cumberland Mountains of Tennessee have 
been carved out of portions of the Appalachian Plateau (Fig. 
290). 



PLAINS AND PLATEAUS 



411 



The line of separation between mountains like the Catskills, and 
plateaus, is not sharply defined, nor is the line of separation between 
plains and plateaus always sharply marked. If you should travel 
westward from the Catskill Mountains, you could not tell the exact 
place where you left the mountains and entered the plateau. If you 
should travel on westward, you could not designate any particular 
place where you left the plateau and entered the Mississippi Plains. 




Fig. 291. — View in the Colorado Plateau, Ariz. 



375. Plateaus of the United States. — The principal pla- 
teaus of the United States are : 

(1) The New England Plateau, the northern end of the 
Piedmont Plateau, which covers nearly all of New England. 

(2) The Southern Piedmont Plateau, including the area 
between the Atlantic Coastal Plain and the old Appalachian 
Mountains. Much of the northern part of this region is more 
truly -plain than plateau, but the southern part of it is mostly 
plateau. Both (1) and (2) consist of an uplifted peneplain, 



412 ELEMENTS OF PHYSICAL GEOGRAPHY 

which is more plateau-like at the north and south ends than in 
the middle portion. 

(3) The Appalachian Plateau, extending south from the 
Lake Plains of central New York to the Coastal Plain of Ala- 
bama and Georgia, and west from the Allegheny Front to the 
plains of the Mississippi. The northern portion is called the 
Allegheny Plateau, and the southern part the Cumberland 
Plateau. 

(4) The Ozark Plateau, extending north from the Boston 
Mountains to the plains of Missouri, and west from the Mis- 
sissippi Plains to the Great Western Plains. 

(5) The Colorado Plateau, extending from the Rocky Moun- 
tains west and northwest to the Great Basin, and southwest 
to the Open Basin region of Arizona (Fig. 291). 

(6) The Columbia Plateau of eastern Washington and Oregon 
and southern Idaho, between the Rocky Mountains on the east 
and the Cascade Mountains on the west. 

(7) The Edwards Plateau of western Texas, at the southern 
end of the Staked Plain. 

(8) The Stockton Plateau, west of the Edwards Plateau, 
between the Pecos River and the Rio Grande. The last two 
really form one plateau, cut in two parts by the Pecos River. 

Besides those mentioned there are several smaller plateaus. 

376. Canyons. — All of the plateaus above mentioned are 
characterized by deep, narrow, cliff-walled valleys, called 
canyons in the west, and gorges, chasms, and glens in the east. 
The canyons of the western plateaus are deeper than in the 
east, because the plateaus are higher, and the streams have 
a greater thickness of rocks to cut through before reaching 
their grade. The western canyons are generally narrower 
and have more rock cliffs because of different climatic con- 
ditions. The weathering agents do not work as rapidly on 
the walls of the canyon as in the moist climate of the east, 
and the concentrated rainfall characteristic of dry climates 



PLAINS AND PLATEAUS 



413 




Fig. 292. — View in the Grand Canyon of the Colorado, Ariz. (Photo by 
U. S. National Park Service.) 



414 



ELEMENTS OF PHYSICAL GEOGRAPHY 




Fig. 293. 



The Grand Canyon of the North Platte River, Wyo. 
■ U. G. Cornell.) 



(Photo by 



PLAINS AND PLATEAUS 



415 




Fig. 294. — Grand Canyon of the Yellowstone in Yellowstone National Park. 
(Photo by B. W. Clark.) 



416 ELEMENTS OF PHYSICAL GEOGRAPHY 

causes more rapid run-off and more concentrated erosion in 
the stream channels. 

The Grand Canyon of the Colorado River is the deepest of 
all the canyons and one of the picturesque wonders of the world 
because of its vastness. The river has here cut a canyon more 
than a mile deep with its sides consisting of rock walls carved 
into varied and. wonderful forms that overwhelm the mind of 
the observer with awe at their size and grandeur (Fig. 292). 

The canyons of the Columbia and Snake rivers in Washington, 
Oregon, and Idaho, and that of the Yellowstone River in Yellowstone 
Park, are second only to that of the Colorado in size and beauty 
(Figs. 293 and 294). 

The White River and the Buffalo River and their tributaries have 
cut many deep canyons or gorges in the Ozark Plateau in Arkansas 
and Missouri, as have the Ohio River and its tributaries in the Alle- 
gheny Plateau in West Virginia, Ohio, and western Pennsylvania, 
and the Susquehanna and its tributaries in central Pennsylvania and 
southern New York (Figs. 290 and 295). 

There are also many large and picturesque canyons in the moun- 
tains, especially in the Rocky, Cascade, and Sierra Nevada mountains. 

377. Plateaus and Man. — In general plateau regions are 
less densely populated than plains. The reasons for this are : 
(1) the deep valleys cut by the streams have lowered not only 
the surface waters, but the water table as well, hence a scarcity 
of water ; (2) the soil is generally less productive ; (3) trans- 
portation is more expensive, in having to contend with heavy 
grades and in crossing deep valleys ; (4) plateaus are colder 
than surrounding plains ; high plateaus especially are affected 
by this difference in temperature. In tropical countries this 
is an advantage, as in the Plateau of Mexico, but in temperate 
regions the high plateaus are too cold for successful farming. 

The Colorado Plateau, the highest of the large plateaus of 
the United States, has a very scanty population, owing to the 
factors above enumerated. The Columbia Plateau has a 
larger population than the Colorado because portions of it 




Tig. 295. — Ausable Chasm, N. Y. (Photo by H. W. Brock.) 
417 



418 



ELEMENTS OF PHYSICAL GEOGRAPHY 



are more plain-like in character, that is, portions of it are not 
deeply trenched by the streams, and the surface is covered with 
a rich soil. In portions of this plateau the valleys have widened 
sufficiently for considerable population in the bottom of the 
valleys (Figs. 296 and 297). 




Fig. 296. — Wheat field on the Columbia Plateau in Eastern Washington. 
(Photo from Spokane Chamber of Commerce.) 



The Edwards and Stockton plateaus of western Texas are 
thinly populated, mainly because of the scanty water supply. 

The Ozark Plateau of Arkansas and Missouri is more thickly 
populated than the higher western plateaus, but less so than 
the bordering plains. The most thickly settled portions of 
the Ozark Plateau are the lower portions of it, bordering the 
plains. The higher portions, near the Boston Mountains, 
are thinly settled. 



PLAINS AND PLATEAUS 



419 



The higher eastern portion of the Allegheny Plateau is more 
thinly settled than the lower western and northern portions, 
bordering the plains. However, a large part of the Allegheny 
Plateau is more densely populated than any other plateau 
region of the United States, because of the rich mineral wealth in 
coal, oil, and gas, in addition to the agricultural and lumbering in- 



Fg^T " £T 



m : . ii» ' WT\ fife. * *i i 



Fig. 297. — Sheep grazing on the Columbia Plateau, Ore. 



dustries, and this greater density of population has in turn caused 
the development of extensive manufactures. The region in and 
around Pittsburgh is one of the great manufacturing districts of 
the world, especially in the production of iron and steel (Fig. 298) . 
The New England Plateau region is thickly settled, but the 
population is not on the plateau but in it, in the valleys, plains, 
and lowlands of the plateau region, that is, the New England 
Plateau is so thoroughly dissected by stream and glacier erosion 



420 



ELEMENTS OF PHYSICAL GEOGRAPHY 



that the worn-down portions or lowlands support a dense 
population. 

Hence we find that while plateaus are less densely populated 
than plains, the lower plateaus support a greater population 
than the high ones, and that the more nearly a plateau ap- 
proaches a plain in character, the denser the population ; like- 
wise the older the plateau and the more it is eroded, the greater 




Fig. 298. — View in the Allegheny Plateau. Loading coal on barges on the 
Monongahela River, Penna. , for shipment to the factories in Pittsburgh. (Photo 
by U. S. Geological Survey.) 

the population. Rich mineral deposits, particularly fuels 
that lead to manufacturing, are important factors in inducing 
people to settle on the region. 



1. 
2. 
3. 
4. 
5. 
wells. 



QUESTIONS 

How do plains differ from plateaus ? 

How do plains become plateaus? 

How are mountains formed from plateaus? 

Name and classify all the plains of the United States. 

Explain how coastal plains are generally favorable for artesian 



PLAINS AND PLATEAUS 421 

6. When was the Potomac River a tributary of the Susquehanna ? 

7. Where is the delta of the Hudson River? 

8. What large delta has been made a rich agricultural area by 
means of irrigation ? 

9. Why are alluvial plains always productive farming regions? 

10. Why are there so few large cities on flood plains in the United 
States? 

11. How do peneplains differ from other plains? 

12. Name the different kinds of treeless plains. Why are they 
treeless ? 

13. Make a list of all the canyons you can find in the United 
States, stating the location of each. 

14. Which is the highest plateau in the United States? Which 
is the most populous ? Which is the highest plateau in the world ? 

15. Why are there more canyons and deeper canyons in the western 
United States than in the eastern? 

16. New England was formerly a plain. What kind? How did 
it differ from the present? 



CHAPTER XIII 

MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 

Mountains are prominent elevations differing from plateaus 
in having narrow summit areas. Mountains are the most 
impressive features of the earth because they seem to dominate 
all of the others. The stupendous forces that have formed and 
fashioned the mountains are most directly evident to the eye, 
and the mind is overawed by their grandeur (Fig. 299). 

They are interesting to the geologist and the geographer because 
the great exposure of rocks to the eye appears to give a deeper insight 
into the earth — to lay open to inspection so much of the earth's 
history. There is no sharp line of separation between certain moun- 
tains, like the Catskills, and adjoining plateaus. Likewise the line 
of separation between mountains and smaller elevations, called hills, 
is an arbitrary one. The Black Hills, which are really mountains, 
are popularly called hills, probably because they seem to be dominated 
by the greater Rocky Mountains farther west. On the other hand 
the Fourche Mountains at Little Rock, Arkansas, are really hills, but 
are popularly called mountains because they dominate the smaller 
elevations of the bordering coastal plain. 

378. How Mountains are Produced. — The mountains of 
the earth are produced by two conflicting forces or sets of forces, 
one of which elevates portions of the earth's crust far above 
their surroundings, and the other, the forces of erosion, which 
first carve and sculpture the elevations into the existing moun- 
tain forms, and in time wear them down to lowlands again. 
Since elevation takes place in different ways and in different 

422 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 423 



■■ 

■ ".« 

v- 

■ ■ 


.-.■.-■ 

■ " : 




^it ' '■ • : -v. ■■•v-"J?^i Sf^ 


§§P^ 


■%s. ; ;■;■■■*/ W" 


■■ . ■ j 



Fig. 299. — Going-to-the-Sun Mountain in Glacier National Park. A moun- 
tain of erosion, carved out of beds of sedimentary rocks. (Photo copyrighted 
by the Kiser Photo Co.) 



424 ELEMENTS OF PHYSICAL GEOGRAPHY 

degrees, and since the erosional forces are of different kinds, 
acting with varying degrees of intensity and on different rocks, 
there are mountains of many kinds, varying widely in size, 
origin, shape, and structure. Following are some of the more 
or less distinct types, based largely on mode of origin and 
structure. 




Fig. 300. — Anticline in the folded Allegheny Mountains. 

379. (1) Folded Mountains. — Many of the great moun- 
tain ranges of the world are folded mountains, in which the rock 
strata are wrinkled or folded somewhat like the leaves of a 
magazine if you should place it flat on a table with outer 
edge against a wall and push the back edge. The uplift may 
be a single upfold or anticline or it may produce a series of 
more or less parallel anticlines, synclines, and monoclines 
(Fig. 300). 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 425 

The Laramie, Big Horn, and Uinta Mountains are examples 
of single anticlinal folds in different stages of erosion. Chestnut 
Ridge and Laurel Ridge in western Pennsylvania are smaller 
and simpler types of the same kind. 

The Allegheny Mountains of Pennsylvania, Maryland, and 
Virginia are examples of the multifold mountains. When the 
mountains were first elevated, the anticlines formed the more 
or less parallel ridges and the synclines the intervening valleys. 
In time the agents of erosion carried away the anticlinal ridges, 
bringing the anticlines and the synclines to a common level. 
Further erosion was more active along the axes of the anticlines 
because the stream channels were already established there, 
the rocks were more fractured, and the edges of the layers 




Fig. 



301. — Synclinal mountains, S S', formed in a region of folded rocks 
by greater erosion on the anticlines, A A'. 



were better exposed for erosion. The more rapid erosion along 
the anticlines left the synclines as the present mountain ridges. 
(See Fig. 301.) 

(a) During erosion of the top of a large anticline which con- 
tains alternating layers of hard and soft rocks, parallel valleys 
developed on the softer layers, leaving the hard layers stand- 
ing up as ridges between the valleys. In this way a succession 
of ridges, a half dozen or more, are carved out of a single anti- 
cline. Sometimes one of the hard layers is more resistant than 
another and forms a higher ridge, a less resistant layer forming 
a lower parallel ridge, which to the observer at a distance looks 
like a .terrace on the side of the higher mountain. Such series of 
ridges are called terraced mountains and occur in a number of 



426 ELEMENTS OF PHYSICAL GEOGRAPHY 

places among the Allegheny Ridges. Tussey Mountain, along 
the south side of Nittany Valley, in central Pennsylvania, is 
such a terraced mountain (Fig. 302). 

The Jura Mountains, the Alps of Switzerland, and the Ouachita 
Mountains in Arkansas are other examples of the multifold moun- 
tains. 



Fig. 302. — Terraced mountain. Tussey Mountain, near State College, Penna. 
(Photo by the author.) 

(b) Zigzag mountains are formed Avhen the folded mountains are 
bent or crumpled lengthwise. These occur in several places in the 
Allegheny Mountains, but are better illustrated in the Ouachita Moun- 
tains. 

(c) Canoe mountains are formed in an anticline or syncline 
when the axis of the fold has a sharp pitch, the axis pitching 
down at the ends in the anticline and up at the ends in the 
syncline ; the first resulting in a form like an overturned canoe, 
and the latter, an upright canoe. Deep erosion in the center 
of such folds produces some unique basins or coves, isolated or 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 427 



cut off from surrounding regions by a mountain rim. People 
dwelling in such isolated coves are likely to retain habits and 




Fig. 303. — Diagram of canoe mountains. The upper figure represents 
those formed in a syncline, the lower figure in an anticline. H H H, hard 
rock. (Drawings after Willis.) 

customs that have become antiquated in more cosmopolitan 
localities. Fine examples of canoe mountains occur in the 
Allegheny Ridges (Fig. 303). 



428 



ELEMENTS OF PHYSICAL GEOGRAPHY 



(d) Domed mountains. Another type of folded mountains 
is that in which the rocks are arched up around or over a limited 
area more or less circular in outline, resulting in a dome-shaped 
elevation. The simplest form of dome is the laccolite, such as 
those in the Henry Mountains in Utah, illustrated in Fig. 304, 





Fig. 304. — Laccolites in Henry Mountains, Utah. Upper figure shows 
section through laccolite before erosion. Lower figure shows by dotted lines 
part eroded, exposing the igneous core. (Drawing after Gilbert.) 



in which an intrusion of igneous rocks has spread out in a mush- 
room or umbrella shape, arching up the overlying strata into 
a dome. Erosion of the overlying rocks or part of them ex- 
poses the inner igneous rock core that formed the dome. 

A more extensive dome is that of the Black Hills, in which 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 429 

a central core of granite and metamorphic rocks has arched 
up a great thickness of sedimentary strata, the top of which 



*M$ 


■nMwL \ 






vfmm 


QraLmil 


Jk h 


iWf : *iH'k 1 ' i 


Will- 

















Fig. 305. 



— Needle mountains. Carved by erosion in the granitic core of 
the Black Hills. (Photo by U. S. Geological Survey.) 



has been deeply eroded, exposing the granite core. Erosion 
on the upturned rocks has carved deep valleys on the softer 



^^^^^2^^^^^^^^^^»"^' *<"*"""»'* Granite core **v*'<'-^^|'><^V^'0?^^^^^^^^^^tei 



Fig. 306. — Cross section of the Black Hills. Top of the dome has been 
eroded. Edges of the harder rocks form encircling ridges, separated by valleys 
carved in the softer rocks. 

layers, leaving the harder ones standing up as ridges, both 
ridges and valleys encircling the central mass, which has also 



430 ELEMENTS OF PHYSICAL GEOGRAPHY 

been deeply eroded and carved into rugged peaks (Figs. 305 
and 306). 

The Adirondack Mountains in New York furnish another example 
of domed mountains, larger and more complex than any of the 
others. The present Adirondacks consist of the remnants of a mass that 
has been elevated several different times and has suffered enormous 
erosion in the ages past, which has laid bare a large area of the deeper 
crystalline rocks (Fig. 307). 




Fig. 307. — View in the eroded granitic core of the Adirondack Mountains. 

380. (2) Eroded Plateau Mountains. — The Cumberland 
Mountains in Tennessee, the mountains of West Virginia, the 
Catskill Mountains of New York, the Boston Mountains in 
Arkansas, and other mountains in Colorado, Texas, New 
Mexico, and Arizona are remnants of eroded plateaus, so much 
dissected by stream erosion that the remnants are mountain- 
like in their ruggedness (Fig. 308). 

381. (3) Block Mountains. — In some places the rocks of 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 431 




Fig. 308. 



Eroded plateau mountains in the Allegheny Plateau, W. Va 
(Photo by U. S. Geological Survey.) 



432 



ELEMENTS OF PHYSICAL GEOGRAPHY 



the earth's crust have been broken into huge blocks which have 
been tilted and elevated so that the upturned edges of the 
blocks form mountain crests. These are known as block 




Fig. 309. — Diagram of block mountains. A type of mountains common 
in Nevada, southeastern Oregon, and eastern California. 

mountains; such are the mountains in southeastern Oregon 
and many of those in the Great Basin region in Nevada and 
California (Fig. 309). The largest of all the block mountains 




Fig. 310. — View of Mt. Rainier, Wash. An extinct volcano, now one of the 

national parks. 

in the United States is the Sierra Nevada Range in California. 
It consists of a huge block four hundred miles long and many 
miles in width, which has been tilted westward in the uplift ; 
the high crest is near the eastern edge, and down the western 




Fig. 311. — Mt. Pitt, a symmetrical volcanic peak on the Cascade Mountains. 
(Photo by Miller Photo Co.) 



433 



434 ELEMENTS OF PHYSICAL GEOGRAPHY 

slope of the uplifted block run the rivers tributary to the Sacra- 
mento and the San Joaquin rivers of the Great Valley of 
California. These torrential rivers, such as the American, 
Tuolumne, Hetch Hetchy, Merced, and Kings, have cut deep 
rocky canyons on the western slope of the mountains. Two of 
these picturesque canyons are included in the beautiful Yosemite 
National Park. 

382. (4) Volcanic Mountains. — Some of the highest moun- 
tain peaks in the world are those which have been built up 
around the crater of a volcano by the rock material that has 
been thrown out and accumulated around the opening. Mt. 
Rainier, Mt. Baker, Mt. Hood, Mt. Shasta, and Lassen Peak, 
some of the prominent peaks on the Cascade Range in the west- 
ern United States, and Mt. McKinley, in Alaska, the highest 
peak in North America, are all volcanic mountains. Two of 
these, Mt. McKinley and Mt. Rainier, have been made national 
parks (Fig. 310). Kilauea and Mauna Loa, two volcanic 
mountains on the Hawaiian Islands, have also been made a 
national park. Popocatepetl and Iztaccihuatl, two of the 
highest mountains in Mexico, and Chimborazo and Aconcagua, 
two of the highest peaks in South America, are volcanic moun- 
tains. There are many others along the cordillera in South 
America and Central America (Figs. 310 and 311). 

Some volcanoes are built up on the sea bottom, the tops of the 
volcanoes forming islands in the sea, such as Mt. Etna in the Medi- 
terranean Sea, the Hawaiian volcanoes, and many others in the Pacific 
Ocean. 

Some of the volcanic mountains, in which the volcano is still active 
or only recently extinct, are fairly symmetrical, conical peaks. When 
the volcano becomes extinct, the eroding agencies carve valleys and 
canyons on the slopes of the mountains, and in time wear them down 
and carry them away as they do all other mountains. Almost all 
those mentioned in the foregoing paragraphs are still conical moun- 
tains, but there, are scores of others in all stages of destruction. Teepee 
Mountain in Wyoming is only the remnant of a former large volcanic 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 435 

mountain. The Marysville Buttes, now a cluster of low hills, are the 
remnants of a former large volcanic peak that used to stand in the 
Sacramento Valley in California. 

Besides the volcanic peaks there have been in places vol- 
canic flows that have built up great plateaus, like those in 
Washington and Oregon and in many places in the Rocky 
Mountains and elsewhere. Some of these volcanic plateaus 
have been eroded into mountain fragments, such as the rugged 
San Juan Mountains in southwestern Colorado, and Table 
Mountains, west of Denver. Laccolites are sometimes consid- 
ered as a type of volcanic mountains. (Fig. 312.) 




Fig. 312. — Eroded plateau mountains, Ouray, in the San Juan Mountains, 

Colo. 

Some mountains are more complex in origin than the more or less 
simple types enumerated above ; for example, the Lewis and Living- 
stone Ranges in Montana consist of a great block of the earth's crust 
that has been uplifted and thrust eastward many miles out on the 
Great Plains. The rocks were folded and crumpled somewhat in the 
movement and were subject to enormous erosion by rivers and glaciers, 
which have carved the whole mass into those wonderful castellated 
peaks and ridges, dotted with lakes, glaciers, and waterfalls, producing 
the sublime scenery of our far-famed Glacier National Park (Figs. 215, 
216, 222, 236, 299, and 313). 

383. Life History of Mountains. — The great mountain 
ranges were born in the sea. They began with the accumu- 



436 ELEMENTS OF PHYSICAL GEOGRAPHY 

lation of a great thickness of sediments on a subsiding sea 
bottom. After a time uplift began, generally accompanied by 
folding. As soon as the strata were elevated above the surface 
of the sea, the agencies of erosion began, slowly at first, but in- 
creasing in intensity with increasing elevation. As long as 
elevation goes on more rapidly than erosion, the mountains 




Fig. 313. — View in the Rocky Mountains in Glacier National Park. Vulture 
Glacier. (Photo by U. S. Geological Survey.) 

continue to grow, but after a long time elevation stops, either 
temporarily or permanently, while erosion continues, and the 
mountains are worn down. 

The youthful stage is the period of increasing elevation, the 
mature stage is at and near the period of maximum elevation, 
and old age is the final period of erosion down to low levels. 
In the early stages of youth the slopes and crests are generally 
rather uniform and regular in outline, but as the mountain con- 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 437 

tinues to grow, valleys form on the slopes and they become 
rugged; waterfalls, canyons, gorges, steep cliffs, and talus 
slopes are formed ; on the higher mountains are glaciers, snow 
fields, avalanches, and landslides. This condition continues 
into and through the mature stage, the period of maximum 
elevation and ruggedness. In this stage the crests become 
sharp ridges and begin to crumble away, faster in some places 
than in others, so that serrated ridges with high peaks result, 
talus slopes increase in size, waterfalls are changing to rapids, 
and the area gradually merges into old age, when the cliffs 
disappear, the slopes become soil covered, the tops of the ridges 
and peaks are lowered, the valleys are areas of deposition, and 
the angularity and the ruggedness of maturity give way to 
rounded, gentler slopes. 

The Adirondack Mountains have passed maturity and show many 
of the characteristics of old age ; Pilot Mountain in Missouri and 
Fourche Mountain in Arkansas show more advanced old age. The 
area about New York City, Philadelphia, and Baltimore represents 
extreme old age, where the mountains have been worn down to low 
hills and plains. This final stage is called a peneplain, and the more 
prominent elevations on the peneplains are called monadnoeks. 

384. Mountain Barriers. — Mountains act as barriers in 
the distribution of moisture. In crossing high mountains, 
moisture-laden winds lose most of the water on the windward 
side and pass down the lee side as drying winds. Thus the 
west slope of the Andes in the trade-wind belt receives almost 
no moisture, as it is nearly all precipitated on the east side of 
the mountains, where it helps to form that greatest river in the 
world, the Amazon. 

The higher the mountain, the more effectual barrier it is to 
the vegetation and the lower forms of animal life. Very few 
of the plants that grow on the plains or in the valleys could by 
natural means cross such mountains as the Rocky Mountains 
or the Andes. Hence the native plants — the wild flowers, 



438 ELEMENTS OF PHYSICAL GEOGRAPHY 

shrubs, and trees — are quite different on the two sides of these 
mountains. The same is true of many animals. Some of the 
hardier and more roving ones find the mountains an obstruction 
indeed, but like man they can and do cross them. 

The difficulties attending the crossing of mountains are frequently 
a decided check to the free intercourse of the people on both sides, and 
the partial isolation in sequestered mountain valleys is liable to cause 
a very provincial community, in which habits and customs of past 
decades are preserved. In many of the deep valleys or coves in the 
Allegheny Mountains one may see the customs of fifty years or more 
ago with little change or modification. In some places the old style 
wagons with wooden axles, linch pins, and tar buckets are still in use. 

385. Mountain Climate. — The climate of mountains is 
different from that of the surrounding plains and valleys. So 
marked are the differences on mountains of even moderate 
height, compared with surrounding lowland areas, as to cause 
a difference of plant and animal life. The climate is likely to 
prove more moist than on the lowlands, but in the region of 
prevailing winds this may prove true of only the windward side 
of the mountains, while the lee side may be dry and barren. 
The east side of the Andes in the trade-wind belt has a very 
heavy precipitation, while the west side is rainless. In the 
Himalayas the north slopes are dry and are bordered by an 
arid region, while the south slopes have an exceptionally heavy 
precipitation, the heaviest in the world. 

The heavy rainfall and snowfall of the mountains are being 
used in many localities in the western United States to furnish 
water for irrigating the surrounding semiarid plains and 
plateaus. The mountains and plateaus are important factors 
in inducing rainfall over the continents. The winds passing 
over the ocean and plains are warmed and absorb moisture; 
in climbing the mountains they are cooled and precipitate the 
moisture. 

The change in temperature found in ascending mountains 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 439 

is quite marked. Not only is the average temperature lower, 
but the daily range in temperature is greater. Night on the 
mountains is always cool and on the highest mountains is al- 
ways cold, even in the summer. 

The decrease in temperature varies somewhat in different localities, 
but the average change found in ascending mountains is a decrease of 
one degree for every three hundred feet of ascent, hence in the tropics 
about the same temperature changes are experienced in ascending a 
high mountain as are found in taking a journey from the equator to 
the north or south pole. For this reason mountains are popular 
summer resorts, where the people from the surrounding plains go to 
find relief from the heat in the summer season. 

386. Economic Features of Mountains. — There is some 
agricultural industry in old mountains, on which the slopes 
have become soil covered, but the amount of farm products 
produced in mountains is very small compared with either 
plains or plateaus. However, the valleys in old and mature 
mountains are often rich farming regions. The Great Valley 
of the Appalachian Mountains, including the Lebanon and 
Cumberland valleys of Pennsylvania and the Shenandoah 
Valley in Virginia, and the Nittany and Bald Eagle valleys 
and other valleys in the Allegheny Mountains, are prosperous 
farming regions, but the bordering mountain ridges produce 
almost no farm crops. 

There are some valleys and plains in the Rocky Mountains 
that contain valuable farm lands, but the mountains themselves 
produce very little. The same is true of the Cascade and the 
Coast Mountains. There is some farming on the old moun- 
tains in New England, and more on the much older, worn- 
down mountains or peneplains around Philadelphia, Baltimore, 
and Washington. 

Lumbering is an important industry in many mountains. 
All the mountains of the eastern United States were covered 
with valuable forests when the country was first settled, but a 



440 



ELEMENTS OF PHYSICAL GEOGRAPHY 



large part of these great forests have been cut over and the 
best of the trees turned into lumber. Small areas in the 
Adirondacks and the southern Appalachians still retain the 
virgin forest (Fig. 314). 

Large portions of all the eastern mountains are still covered 
with woods, and efforts are now being made to conserve the 




Fig. 314. — On the Hudson River near Glens Falls, N. Y. Spruce logs on 
the way to the paper mill, indicating the rapid destruction of our forests. 
(Photo from National Geographic Magazine.) 



remnants of our former large forests. Most of the mountain 
land is unsuited to agriculture, and many portions that were de- 
forested and burned over were left as barren wastes. Efforts 
are being made to cover these mountain slopes with a new 
forest growth. A large part of the Adirondack Mountains is 
now owned by the State of New York and included in the forest 
preserve. The same is true of the Catskill Mountains. The 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 441 

forest remnants are protected from fire, and in time the 
growth of young trees will form new forests. The treeless 
portions are being planted with young trees by the foresters. 
Part of the southern Appalachians are now portions of the 
national forest. Pennsylvania and some of the other states, 
as New York, are endeavoring by planting and protec- 




Fig. 315. — New forest growth replacing the trees removed by the lumbermen. 
(Photo by the U. S. Bureau of Forestry.) 



tion to get the barren mountain slopes covered with forests 
(Fig. 315). 

In the western United States climatic conditions are different 
from the eastern part of the country. There is not sufficient 
rainfall on the plains to support tree growth, hence the forests 
of the west and middle west are largely confined to the mountain 
slopes that have sufficient precipitation. In the extreme north- 
western part of the country, in western Washington, in Oregon, 



442 



ELEMENTS OF PHYSICAL GEOGRAPHY 



and in northern California, there is sufficient moisture for forests 
in the valleys, but in southern California, in the Great Basin, 
and in the greater part of the Rocky Mountain area the lowlands 




Fig. 316. — View above the cold timber line in the San Juan Mountains. 
Shows glacial cirque, terminal moraine, and moraine talus cone. (Photo by 
the author.) 



are treeless. The lower limit of forests on the western moun- 
tains is called the dry timber line. In the southwest this dry 
timber line is 6000 to 8000 feet above sea level, and the base of 
the mountains below these heights is devoid of forests. In the 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 443 

northern Rocky Mountains the dry timber line descends to 
4000 to 5000 feet. 

The high mountain crests and peaks of the Rocky, Sierra 
Nevada, and Cascade Mountains extend above the cold timber 
line and are treeless because of the excess of snow and low 
temperatures. Hence, on the western mountains the forests 
occur on the slopes between the upper cold timber line and the 
lower dry timber line. These forest belts are wider in the 
north than in the south because there is greater precipitation 
in the north (Fig. 316). 

The heaviest forests, in fact the densest forests in the United 
States, are on the western slopes of the Coast, Cascade, and 
Sierra Nevada Mountains. Most of the western mountains 
are now in the national forest under the control of the United 
States government. 

Mining. The minerals that occur in veins, that is, filling 
cracks or fissures in the earth's crust, are mined most ex- 
tensively in mountains, because deep erosion exposes the edges 
of a greater thickness of rocks than is found in plains and 
plateaus, and the fracturing and metamorphism of the rocks 
during the formation of the mountain produces more veins and 
greater concentration of vein-forming minerals than in areas 
of undisturbed rocks. 

Much of the gold, silver, lead, zinc, copper, mercury, and 
tungsten mined in the United States is obtained in the moun- 
tains. Many ranges of the Rocky Mountains and the central 
mass of the Black Hills, the Sierra Nevadas, and the mountains 
of central and southern Arizona and Utah have rich mineral 
deposits and extensive mines (Fig. 317). The mineral pro- 
duction of the Cascade Mountains is not large. The Boston 
Mountains and the Ouachita Mountains produce very little 
mineral wealth. The anthracite coal field of eastern Pennsyl- 
vania-occurs in the Allegheny Mountains, but south and west 
of the Susquehanna River there is no mineral wealth of any 



444 



ELEMENTS OF PHYSICAL GEOGRAPHY 



value in the Allegheny Mountains, except one small coal field 
(the Broad Top) in central Pennsylvania. The great bitumi- 
nous coal fields of the east occur in the Appalachian Plateau. 
Most of the coal, petroleum, and natural gas of the United 
States occurs outside of the mountains. 























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Fig. 317. — Placer mining in the Sierra Nevada Mountains, Calif, 
the U. S. Geological Survey.) 



(Photo by 



The Catskill Mountains are almost devoid of mineral wealth. 
The Adirondack Mountains of New York and the mountains 
of New England contain granite, marble, and slate quarries, 
some iron mines in the Adirondacks, and small quantities of 
other minerals, such as graphite, asbestos, talc, and garnets, 
but the mineral wealth of these mountains is not great. 

Water Power. The streams flowing from mountains mostly 
flow down steep grades and because of heavy precipitation 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 445 

carry large volumes of water, hence furnish a source of enormous 
water power. Until recent years this power was not much used, 
because the cities and factories that needed the power are 
generally some distance away from the mountains. The 
development and improvement of hydro-electric power, in 
which the water power is changed to electric power, capable of 




Fig. 318. 



Grazing in the Uinta National Forest, Uinta Mountains, Utah. 
(Photo by U. S. Bureau of Forestry.) 



being transferred long distances by. wire, has led to the greater 
utilization of the water power of the mountain streams. The 
increasing price of coal and the fact that the railways cannot 
transport it in sufficient quantities to meet the needs of the 
country, are additional factors tending to a greater use of the 
abundant water power of the mountains. One of the trans- 
continental railways (the Chicago, Milwaukee and St. Paul) 



446 



ELEMENTS OF PHYSICAL GEOGRAPHY 



is now using water power to move its trains across the Rocky 
Mountains. No doubt many other railways will soon utilize 
the water power where it is available. As yet only a very 
small portion of the available water power is used. 

Grazing Grounds. The western mountains are utilized as feeding 
grounds for herds of cattle, sheep, and horses. The forest belts and 




Fig. 319. — Camp scene in the Adirondack Mountains. The mountains are 
delightful places for recreation in the warm season. (Photo by the author.) 



the grass lands bordering the forests furnish excellent grazing lands. 
Even the National Forests are so utilized under government restric- 
tions (Fig. 318 and Frontispiece). 

Recreation. One of the most important uses of the mountains to 
man is for recreation. The pure air and water and the picturesque 
scenery, the cool summer temperature, and the fish and game make 
the mountains great natural parks and places of rest and recrea- 
tion for the people of the plains, and each summer finds larger 
and larger numbers of the plains people going to the mountains (Fig. 
319). 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 447 

Mountains are likewise sources of pure water and pure air to the 
people of the bordering plains and valleys. They furnish pure water 
not only for the household, but also for irrigation. 

387. Special Topographic Features. — There are some minor 
subdivisions of the great topographic features of plains, plateaus, 
and mountains that merit consideration. Canyons were de- 
scribed in Sec. 376, glacial moraines, drumlins, eskers, and 
kames were described in the chapter on glaciers (Sees. 308, 320, 




Fig. 320. — Edge of a mesa or table-land in Utah. (Photo by B. W. Clark.) 

321, 322), sand dunes in Sees. 166, 167, 168. Other specialized 
forms are mesas, buttes, hogbacks, palisades, sand hills, bolsons, 
playas, mud lumps, and buffalo wallows. 

388. Mesas. — Mesas or table-lands are small plateaus, or 
fragments or remnants of plateaus, left by erosion. They are 
largely limited to the arid or semiarid regions of the west and 
southwest. They are flat-topped hills whose surface areas 
vary from a few acres to many square miles in extent. They 
are striking features in western Texas, New Mexico, Arizona, 
Utah, southern Colorado, and Wyoming (Fig. 320). 



448 ELEMENTS OF PHYSICAL GEOGRAPHY 




Fig. 321. — A butte; edge of mesa on the right. (Photo by W. B. Heroy.) 



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Fig. 322. — Hogback ridge, foothill of the Rocky Mountains. 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 449 

389. Buttes. — Buttes are prominent hills or peaks of smaller 
area than a mesa, in fact many of the buttes are erosional rem- 
nants of mesas. Like the mesas they are features of the arid 
and semiarid regions (Fig. 321). 

390. Hogbacks. — Hogbacks are sharp-crested ridges formed 
by erosion on the upturned edges of hard strata bordering uplifted 




Fig. 323. — Crest of one of the "flatirons," a special type of hogback topog- 
raphy at Boulder, Colo. The upturned hard rocks rest directly against the 
granite core of the mountains. 



mountain areas, like the Black Hills and many of the ranges oi 
the Rocky Mountains. They commonly occur as foothills to 
higher mountains and are best developed along the Front Ranges 
of the Rocky Mountains through Colorado. They generally 
have a steeper slope facing the bordering mountains, with a gen- 
tler slope towards the bordering plains. If the strata are turned 
up nearly perpendicular the hogback may be symmetrical, with 



450 



ELEMENTS OF PHYSICAL GEOGRAPHY 



equal slopes. A special form of the hogback is that where the 
hard layer rests directly against the hard rocks of the central core 
of the mountain, with no intervening soft layer. Such are the 
" Flatirons " at Boulder, Colorado (Figs. 322 and 323). 

391. Palisades. — Palisades are the exposed edges of basaltic 
layers in the midst of other rocks on the face of steep cliffs. 




Fig. 324. — Buffalo wallow on the Great Western Plains of western Kansas. 
(Photo by U. S. Geological Survey.) 

They most commonly occur on the cliffs bordering a river which 
has cut down through the mass of rocks inclosing the basaltic 
layers. The best known examples are the Palisades of the 
Hudson River above New York City. Similar palisades occur 
along the Connecticut River, and the Columbia River in Oregon. 
They also occur in the lower canyon of the Yellowstone River 
in Yellowstone Park. The Giant's Causeway is the upper sur- 
face of a similar basaltic rock on the coast of Ireland. (Fig. 272.) 



MOUNTAINS AND MINOR TOPOGRAPHIC FEATURES 451 

392. Mud Lumps. — Low mounds of small area are formed over 
the surface of the lower Mississippi Delta by the upswelling of the 
muds and silts of the delta. Such mounds are called mud lumps. 

393. Buffalo Wallows. — Shallow, basin-like depressions occur on 
the Great Plains ; these depressions are supposed to have been formed 
by the buffalo or bison which came to these spots to wallow in the soft 
muds during the wet season (Fig. 324). 

394. Playas. — Playas are broad, very shallow basins occurring 
in the arid and semi-arid regions. They are probably formed by the 
wind blowing the dust from these areas. Occasionally they are covered 
with water after a heavy rain, but the water soon evaporates, leaving 
first a mud flat, which commonly becomes a dust plain. They are 
characteristic of deserts. (See Fig. 253.) 

395. Bolsons. — Bolsonsare larger, deeper basins than playas and 
are commonly partiaUy, or sometimes entirely, surrounded by moun- 
tains. They are interior basins in a mountainous or hilly desert 
region. They are most abundant in western Texas. 

QUESTIONS 

1. How do mountains differ from plateaus? From. hills? 

2. Make a list of all the mountain ranges you can find in the 
United States., with the location of each. 

3. Draw a cross section and longitudinal section of an anticlinal 
canoe mountain containing two hard beds. 

4. Why do nearly all the large rivers of the Sierra Nevada Moun- 
tains flow west? How does the scenery of the slopes differ? 

5. Mt. Etna is only 10,758 feet above the level of the sea, but it 
is a larger and higher mountain than Mt. Hood in Oregon, although 
the top of the latter is 11,225 feet above the sea. Explain how the 
lower mountain is the higher. 

6. How are table mountains formed ? What is a butte ? 

7. Name some plants that, without the aid of man, would find 
mountains, such as the Rocky Mountains, a barrier to their mi- 
gration. 

8. Philadelphia used to be larger than New York City. Why is 
it not as large now? What did the Allegheny Mountains have to 
do with the change? 

9. Why is it colder on mountains than in valleys ? 

10. . Why do so many people of the United States spend a few days 
or a few weeks every summer in the Rocky Mountains in Colorado ? 



452 ELEMENTS OF PHYSICAL GEOGRAPHY 

11. Why are there more national parks in the Rocky Mountains 
than in the Alleghenies ? 

12. What is a timber line? Why are there two timber lines on 
some mountains ? Why is there no timber line on the Catskill Moun- 
tains ? 

13. Why are forest trees planted on the Adirondacks and the 
Allegheny Mountains? 

14. What mineral products come mostly from mountain areas? 
What ones are obtained mostly from plains and plateaus ? 

15. Why is the water power in the mountains used so much more 
now than it was fifty years ago ? 



CHAPTER XIV 

GEOGRAPHY OF PLANTS, ANIMALS, AND MAN 

396. Influence of Environment on Life. — All forms of life 
are of necessity influenced by their physical environment. The 
kind, the abundance, the variety of living forms on any area 
largely depends upon the geographical conditions of soil, climate, 
and topography on the land; and temperature, depth, and 
clearness of the waters in the sea. This has been mentioned 
from time to time in the preceding chapters, but it seems fitting 
now in conclusion to consider the subject directly in reference 
to the life relations. 

Man is probably as nearly independent of his geographical 
surroundings as any other form of life, but it is apparent to all 
that he has been greatly influenced by geographical conditions, 
in his migrations, civilization, and industries, and in his mental 
as well as physical development. Many of the lower forms of 
life are more susceptible than man to their surroundings and 
hence occupy only a few limited areas, while man ranges over 
the earth from the equator to the poles. 

397. Effect of Climate. — There are striking differences in 
the kinds of life and the habits of the living forms in the different 
climatic zones. In the warm, humid region, life, death, and 
decay go on with striking uniformity and rapidity throughout 
the year and the years. In the cold temperate zones there is 
a warm season of rapid growth, and a cold season of rest, when 
the trees, except the evergreens, and the shrubs shed their leaves 
and fruit, and the herbs and grasses die and disappear, all but 

453 



454 



ELEMENTS OF PHYSICAL GEOGRAPHY 



the roots, bulbs, and seeds. Many of the animals hibernate. 
Man, the domestic animals, and some of the wild animals 
remain active during the cold weather of the winter months, 
but the lower forms of life — many of the animals, and all the 
vegetable forms — lie relatively dormant and inactive until 
the return of warm weather. (Fig. 325.) 




Fig. 325. — Winter scene in the forest in temperate climate. Winter is a 
scene of quiet in the forest, when much of the life is dormant. (Photo by the 
New York State College of Forestry.) 



The winter in cold climates is characteristically a season of silence. 
At a distance from human habitations almost the only sounds are 
those of inanimate nature. 

" With the coming of the spring there is a marvelous awakening 
and unfolding. The brooks, swollen to overflowing by the melting 
of the snow, make music as they run. The northward flight of the 
birds brings to every grove a chorus of song. A host of batrachians 
and reptiles bestir themselves after a long winter sleep and vocifer- 



PLANTS, ANIMALS, AND MAN 



455 



ously proclaim their presence. The insect world, with its unnumbered 
legions, takes wing. The air vibrates with millions of voices. The 
trees put forth their leaves, each a harp-string which responds to the 
touch of the fingers of the wind. The organ notes of the thunder 
again startle the hibernating echoes. As the winter is the silent 
season, so the spring is the time of music." — Russell's North America, 
pp. 296-297. 

PLANT GEOGRAPHY 

The number and kinds of plants on any area not under cul- 
tivation are determined largely by the condition of the soil, 
water, air, and temperature. 




Fig. 326. — Spanish moss (an epiphyte) growing on a live-OE 
fels, Tex. (Photo by W. L. Bray.) 



tree, Braun- 



398. Soil. — Most land plants have roots which find anchor- 
age in the soil, from which they derive sustenance both in water 
and mineral matter. While but a small part of the plant is 
formed by the mineral matter in the soil, that small part is so 



456 



ELEMENTS OF PHYSICAL GEOGRAPHY 



important that if the materials are not in the soil the vegetation 
does not flourish. Thus, a grain of wheat that on poor soil 
would sprout and grow a spindly stalk a foot high with no 
grains would on a fertile soil grow a lusty stalk four feet high, 
with many good grains. 

The kind of soil has much to do with the variety and quantity of 
vegetation. Thus the vegetation on a sand soil will be different from 




Fig. 327. — ■ Some types of water plants at Bronx Park, New York City. 
(Photo by W. L. Bray.) 

that on a clay, loam, humus, or alkaline soil. Much depends on the 
relation of these soils to each other ; thus a humus on sand would be 
different from a humus on clay. Just as important as the chemical 
properties are the physical ones, such as the fineness of the particles 
and the porosity of the mass, as affecting the circulation, absorption, 
and retention of moisture. Some forms of life are independent of the 
soil, such as floating vegetation, which derives sustenance wholly from 
the water and air. A few land plants live without contact with the 



PLANTS, ANIMALS, AND MAN 



457 



soil and derive sustenance wholly from the air. Such are called 
epiphytes, because they grow upon the stems and branches of other 
plants. They are most abundant in the tropics. The Spanish moss 
is an epiphyte that grows in great abundance on the live-oak trees in 
the southern and southwestern United States and in Europe. Many 
of the tropical orchids are epiphytes (Fig. 326). 



wf/ jHHH 




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BBS? '^H 





Fig. 328. 



Types of water vegetation in Dismal Swamp, Va. 
U. S. Geological Survey.) 



(Photo by 



399. Water. — Water forms a large part of the material of 
nearly all plants and hence is essential to their existence. The 
kind of water, whether fresh, salt, or alkaline, and the quantity 
of it, whether an excess as in the marsh, a dearth as in the 
desert, a limited supply as in the semiarid districts, or a 
generous amount as in the humid districts ; and the tempera- 
ture, whether hot, temperate, or cold, determine in a large 
degree the kind as well as the quantity of vegetation. The 
distribution of the rainfall, whether e.g. it falls in the winter 



458 ELEMENTS OF PHYSICAL GEOGRAPHY 

or in the growing season, or throughout the year, is important. 
The relation of the water table to the surface soil is also an 
important factor. 

Classification of Plants Based on Water Supply. — On a 
basis of humidity, plants are divided into (1) water plants 




Fig. 329. — Cypress trees and knees in Dismal Swamp, Va. (Photo by U. S. 
Geological Survey.) 



(Hydrophytes), (2) drouth or desert plants (Xerophytes), 
(3) intermediates (Mesophytes) . 

400. (1) Water Plants. — Some water plants grow on the sur- 
face of the water, others on the bottom. Another class includes 
those with the roots on the bottom and the leaves and branches 
above the surface, such as the mangrove tree, water lilies, cat- 
tails, spatter-dock, reeds, and cane in lakes and swamps. The 
water hyacinth is a floating plant that grows in such quantities 



PLANTS, ANIMALS, AND MAN 



459 



on the rivers and lakes of Florida as to be a serious menace to 
navigation and the fishing industries on the inland waters. 
(Figs. 327 and 328.) 

Cypress trees, which grow sometimes in the water and sometimes 
on dry land, develop a unique method of getting air to the roots that 
grow under the water, by having a knob or process grow up through 
the water to and above the surface until it is in contact with the air. 
These knobs, which are known as "knees," stand above the surface, 
looking much like stumps. (See Figs. 329 and 330.) After the drain- 
age of the swamp the new growth of cypress on the dry land is devoid 
of knees. 




Fig. 330. — Illustrating the function of cypress knees. A, level of water in 
wet season ; B, lowest level of swamp water ; a, cypress tree with part of the 
roots under water ; b, tree with all roots under water ; c, tree with none of the 
roots under water ; dd, cypress knees through which the roots breathe ; ee, knees 
not yet grown to serviceable height ; //, abortive knees not needed by the tree. 
(After Shaler.) 

The sargassum that occurs so abundantly out in mid-ocean has 
numerous small air sacs which serve as floats or life preservers to keep 
it at the surface. The bladderwort, a fresh- water plant, has similar 
floats. The bladders or air sacs serve to aerate the plant, as well as 
float it. The duckweed, a small green floating plant, has numerous 
air chambers through the body of the plant. There is another class 
of water plants, microscopic in size, that occurs in vast quantities in 
both salt and fresh water. The best known forms in this class are the 
diatoms, which secrete a wall of silica and hence are preserved in great 
deposits on the bottom of the sea and lakes. 

There is a prolific flora on the shallow sea bottom over a 
large part of the continental shelf. This growth is greatest 
in tropical and subtropical seas. A trip in one of the glass- 
bottomed boats at Catalina Island, off the California coast, 
gives one a view of the vegetation in these " submarine gardens" 



460 



ELEMENTS OF PHYSICAL GEOGRAPHY 




that he will not soon forget. 
The multitude and variety 
of plants, large and small, 
with their varied colors and 
the swarms of fishes and 
other forms of sea life, makes 
an ever-changing picture of 
wonderful beauty. 

401. (2) Desert Plants. — 
Drouth or desert plants have 
the opposite conditions from 
the water plants, namely, 
scarcity of water instead of 
an excess. The differences 
are strongly marked both in 
quantity and kind. One of 
the striking features of 
deserts is the scarcity of life 
both plant and animal. 
Another feature is the marked 
difference in the kinds of 
plants as compared with a 
wet or humid area. Through 
successive generations, desert 
plants have in different ways 
adapted themselves to arid 
conditions so as to conserve 
the little, moisture they ob- 
tain and prolong their exist- 
ence through long periods 
without rain (Fig. 331). 

One striking feature of des- 
ert vegetation is the scarcity 
of leaves. Some plants have 



PLANTS, ANIMALS, AND MAN 



461 



no leaves. On some plants the leaves have a hairy covering 
that serves to protect them from the burning sun. Most of 
the desert plants are covered with thorns or prickles. Some 
plants, like the barrel cactus, have special means of storing 
water for the dry season (Fig. 333). 

Cactus, sagebrush, greasewood, and yucca are among the most 
common plants on our western desert (Figs. 332, 333, and 334). 

The semiarid regions have a greater variety and number of plants 
than the desert. In such areas some of the plants conserve moisture 




Fig. 332. 



Desert vegetation: mesquite, cactus, sagebrush, etc., in Arizona. 
(Photo by D. T. McDougal.) 



by curling the leaves and thus exposing a smaller surface to the sun. 
Some lie dormant during the dry season, just as others do in the cold 
winter season. 

402. (3) Intermediate Plants. — The intermediate plants, 
which grow on dry land supported by a fairly abundant rain- 
fall, are the most numerous, and comprise about eighty per 
cent of the total flora. They are called mesophytes because 
they- occur midway between the very dry and th3 very wet 
conditions. They include most of our cultivated plants and 



462 



ELEMENTS OF PHYSICAL GEOGRAPHY 



most of the forest trees. They occur in the same rain belts 
as the water plants, but under different physiographic con- 
ditions, that is, they grow where there is sufficient rainfall, but 

the water does 
not stand on the 
surface in 
swamps, lakes, 
and oceans, as in 
the case of the 
habitat of the 
hydrophytes. 

They occur in 
different rain 
belts from the 
desert plants. 
The dividing line 
is about twenty 
inches annual 
rainfall, that is, 
an area with less 
than twenty 

inches is semi- 
arid to arid. It 
varies consider- 
ably with the dis- 
tribution of the 
rainfall and other 
conditions. It 
requires about 
twenty inches of 
annual rainfall to support forest growth, but under certain condi- 
tions some coniferous trees exist in cold climates on less than that. 

The slopes of the Rocky Mountains are covered with forests (where 
they have not been destroyed) which form a belt between the plains 




Fig. 333. — Barrel cactus, a desert plant that stores 
water. Sonora, Mexico. The Papago Indian has 
broken off the top, crushed the pulp, and is drinking 
the water. (Photo by D. T. McDougal.) 



PLANTS, ANIMALS, AND MAN 



463 



at the base, treeless from the lack of rainfall, and the treeless peaks 
at the top made so from excess of snOw. On all very high mountains, 
even in the tropics, there is an upper limit to tree growth known as 
the timber line. (See Figs. 313 and 316.) 

The upper limit of trees is not always due directly to cold, but 
sometimes to excess of snow, as shown by the occurrence of trees on the 
narrow ridges much higher than in the depressions. It is in the de- 




Fig. 334. — Oasis in the Colorado Desert near Indio, Calif. Any part of a 
desert area with water at or near the surface is an oasis, a green spot in the 
midst of a brown waste. (Photo by D. T. McDougal.) 



pressions where the snow accumulates and remains long after it 
has melted from the ridges, so that the growing season, when the 
ground is free from snow, is too short for trees to develop. 

In respect to their association, there are two great groups of 
the intermediate plants that have a very pronounced effect on 
the surface. "The one group consists of grasses and herbs and 
forms the meadows, prairies, and pastures. The other consists 
of shrubs and trees and forms the thickets and forests (Fig. 335) . 
With change of conditions each of these may encroach upon the 



464 ELEMENTS OF PHYSICAL GEOGRAPHY 

territory of the other. Fig. 336 shows an area in Texas where 
the forest trees are now advancing over the grass plains. The ax 
and forest fires have been instrumental in changing thousands of 
acres of forest area to grass land, or in some cases to waste land. 




335. — Big thicket vegetation on the coastal plain in Texas. (Photo by 
W. L. Bray.) 

Where man protects the grass plains from fire and does not culti- 
vate the soil, there the trees spread out on the plains. (Fig. 336.) 
Generally speaking, farm crops do not mature with less than 
twenty inches of annual rainfall. Yet there are some exceptions, 
as where most of the rain falls during the growing season, and 
by special methods of dry farming crops are raised with less 
than twenty inches of rain. 



PLANTS, ANIMALS, AND MAN 



465 



403. Air and Light. — A large supply of the raw materials 
for plants is derived from the air, and consists largely of car- 
bonic acid, which in the cells of the green plant is decomposed, 
the carbon with some oxygen and hydrogen forming compounds 
which make up the plant tissue, while some of the oxygen is 
set free. The nitrogen of the plant comes from the soil, but 
the soil probably obtained it originally from the air. 




Fig. 336. — Forest trees encroaching on the prairie on the coastal plain in 
Texas. (Photo by W. L. Bray.) 



All green plants require light. Green cells are food factories where 
water, materials from the soil, and carbon dioxide and other gases 
of the air are combined to produce food for plant tissue which supplies 
food for animals or for other plants. The sunlight and the green 
material (called chlorophyll) of the plant cell seem to be the most 
important factors in this little organic laboratory where the inorganic 
air and mineral matter are changed to the organic vegetable com- 
pounds. The plant tissue which is eaten by animals undergoes further 
changes in the chemical laboratory of the animal which devours it, 
and is there transformed to animal tissue. Some plants, known as 
light plants, require more light than others, which are known as shade 
plants. In a forest there are several zones or strata based on the rela- 



466 



ELEMENTS OF PHYSICAL GEOGRAPHY 



tive amount of light. The tall trees form the upper zone and receive 
the most light, below this is a stratum of shrubs, then herbs, and next 
to the ground the green mosses and lichens. (See Fig. 337.) 

404. Temperature. — The extremes of temperature between 
which nearly all plants grow are 32° and 122° F. Some forms 
of algse live in the Hot Springs of Yellowstone Park at a tem- 



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H \ 




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Fig. 337. — Tree and shrub zones in forest on Mt. Mitchell, N. C. 
by U. S. Bureau of Forestry.) 



(Photo 



perature as high as 199°. By a special adaptation to change 
of conditions, plants lying dormant pass through cold 
winter seasons having a temperature much below 32°. The 
distribution of the temperature throughout the year, and the 
relation of the temperature to moisture, are important factors 
to consider. 



PLANTS, ANIMALS, AND MAN 



467 



A general subdivision of the land area into plant zones, based on 
temperature, is sometimes made into tropical, subtropical, warm tem- 
perate, cold temperate, and cold or polar; but since other factors be- 
sides temperature have a strong influence on the control of plant life, 
such a classification has little value. 




Fig. 338. — Hart's tongue fern grows in Onondaga County, N. Y., on the 
Onondaga limestone only. Common in parts of Europe, but known in only 
one other locality in the United States. (Photo by J. E. Kirkwood.) 



405. Local Zonation. — There are many local zones of veg- 
etation or plant colonies, some based on temperature, some on 
moisture, some on dependence upon other plants, some on 
light, and others on the kind of soil or rock. Certain plants at 



468 ELEMENTS OF PHYSICAL GEOGRAPHY 

times show a very peculiar distribution. The hart's-tongue 
fern (Fig. 338) occurs in Onondaga County, New York, in a few 
places only on the Onondaga limestone. It is not known to 
grow on any other rock in the county ; nor is it known to occur 
in any other place in eastern United States except one place in 




Fig. 339. — Zonal vegetation at Lake Piseco, N. Y. Certain grasses and 
raeds in the lake, other reeds and shrubs in the bordering marsh, fringed with 
a zone of bushes, and next the forest trees. See also Fig. 247. (Photo by the 
author.) 

Tennessee. It occurs in Ontario and is common in North Africa 
and southern Europe. 

Almost all large hills and mountains are belted with different kinds 
of plants or trees, the belts being very irregular in many places, as 
the zones are determined in part by the temperature due to elevation, 
in part by light and wind, in part by the kind of soil. Almost all 
swamps and some lakes have concentric zones based upon the depth 
of the water (Figs. 247 and 339). 



PLANTS, ANIMALS, AND MAN 469 

406. Control of Plant Distribution by Methods of Mi- 
gration. — On areas in which the temperature and humidity 
favor vegetation, the plants must be distributed over the area 
in some way. In the first uplift of a lake bed, a coastal plain, 
or an island area, there may be no vegetation, since the water 
plants are all killed as soon as the water is drawn off. Seeds 
of land plants spread over it in various ways as follows : 

(1) Some are carried by the wind. Some seeds, like those of the 
thistle and dandelion, have feathery floats which serve as little balloons 
to buoy up the seed so that it is carried long distances before it falls 
to the earth to sprout and start a new center of distribution. 

(2) Some seeds have spines or sharp prongs by which they are 
attached to the fur or hair of animals, or the clothing of persons, and 
thus carried to distant points. Such are the burdocks and Spanish 
needles. 

(3) Edible seeds or seeds in edible fruit are often carried by birds 
or other animals to distant points, and there grow and multiply. 

(4) .Some plants have explosive seed pods that fly open with force 
and throw the seeds some distance away. A repetition of this process 
from year to year carries the plants over wide areas. Study the com- 
mon witch-hazel. Many plants migrate or spread by sending out shoots, 
runners, or underground stems. The strawberry is a good example. 

(5) Seeds and sometimes plants are carried long distances by 
rivers and ocean currents. Many oceanic islands obtain their plants 
in this way. The seeds of the cocoa palm are thought by some to 
have been widely distributed by the ocean currents among the coral 
islands of the tropical Pacific Ocean. 

(6) Man is one of the most important agents in distributing plants. 
He transplants them to distant parts of the world, over mountains 
and across oceans or deserts. The food and flowering plants are 
carried to all lands for cultivation, and the seeds of weeds and other 
undesirable plants are unavoidably carried with them. The rail- 
roads and automobiles are important agents in this distribution. 

Forests 

One of the most important topics now before the American 
people is that of the present, past, and probable future con- 
ditions of the forests. When this country was first settled by 



470 



ELEMENTS OF PHYSICAL GEOGRAPHY 




Fig. 340. — View taken in a National Forest in Oregon. (Photo by U. S. 
Bureau of Forestry.) 



PLANTS, ANIMALS, AND MAN 



471 



white men a large portion of it was covered by dense forests. 
The early settlers chopped down the trees and burned them 
in order to clear the land for their farms. Later the lumber- 
men cut the trees by millions to furnish the lumber to build 
the cities, villages, factories, etc. So rapidly has cutting 
of the forests been carried on that extensive areas are 




Fig. 341. 



- Effect of forest fire on an area that has been cut over. 
Mitchell, N. C. (Photo by U. S. Bureau of Forestry.) 



On Mt. 



now bare and barren wastes, for the destruction begun by 
the chopper has been completed by the fires (Figs. 340, 341, 
and 342). 

407. Effects of Forest Destruction. — On most of the 
plateau, plain, and valley areas, after the cutting of the forest, 
the land was brought under cultivation, and is now covered 
with prosperous farms, but in the rocky portions of the 



472 ELEMENTS OF PHYSICAL GEOGRAPHY 

mountainous and hill country the slopes are so steep and 
the soil is so thin or so poor that it cannot be cultivated, 
and the result is that unproductive and unsightly barren 
waste areas now mark the sites of former stately forests. 
(Fig. 341.) 




Fig. 342. — Fighting forest fires in the Adirondack State Forest. (Photo by 
U. S. Bureau of Forestry.) 



In the virgin forests there was an accumulation of decaying 
vegetation that furnished a rich soil for the forest trees. The 
fires following the cutting of the trees burned up the vegetable 
mold, leaving bare rocks in place of the former deep, rich 
carpet of moss and shrubs. 

The vegetable carpet of the forest acts like a great sponge 



PLANTS, ANIMALS, AND MAN 473 

which absorbs and holds the rainfall, serving to keep the area 
moist in the drier season. The destruction of the vegetable 
sponge causes most of the rainfall to run over the rock surface, 
and thus wash into the streams and carry away the residue 
left by the fire and drouth. (Fig. 342.) 

The absence of the forest permits more of the rainfall to run 
directly into the streams, producing great floods, which means 
destruction to property in the valleys and great decrease in 
farm products from drouth in the dry seasons. 

The preservation and protection of forest areas on the hills, moun- 
tains, and plateaus is of vital importance to the prosperity of the 
farms in the valleys as well as the farms on the upland. 

The chief products obtained from the forests are lumber, wood 
pulp, bark for tanning, pitch, tar, and turpentine. The smaller trees 
furnish telegraph and telephone poles, ties for railways, pulp for paper, 
and wood for charcoal. All of these materials are necessary in our great 
commercial industries, but the method of obtaining them has been 
wasteful and extravagant in the extreme. Now when it is almost 
too late to remedy it, we are beginning to realize that these products 
could have been obtained without the enormous waste. 

State and national legislatures have at last been aroused to 
the importance of preserving or conserving the remnants of 
our former great forests for the welfare, not only of future 
generations, but of the present as well. We now have con- 
siderable areas of forest land owned and controlled by the 
nation and the different states, from which the lumber and other 
products of the forest are obtained without the destruction 
of the forest. The accompanying map shows the location 
of the present national forest preserves of the United States. It 
is to be hoped that these preservations will increase in size 
and number from year to year. Schools of forestry have been 
established for the training of men properly to care for these 
forests and the plant and animal crops which can be derived 
from them. (Fig. 343.) 



474 ELEMENTS OF PHYSICAL GEOGRAPHY 




Fig. 343. — Map of the National Forests of the United 



PLANTS, ANIMALS, AND MAN 



475 




States. ' (Map from U. S. Bureau of Forestry.) 



476 



ELEMENTS OF PHYSICAL GEOGRAPHY 



408. Forests in the United States. — The principal forest dis- 
tricts of the United States from which enormous quantities of lumber 
have been obtained, and which still contain forest remnants of great 
value, are : 

I. New England, including Maine, New Hampshire, and Ver- 
mont, with their great forests of pine, hemlock, spruce, and cedar, 
and smaller forests of oak, maple, birch, elm, etc. 




Fig. 344. — Example of poor forestry : waste of much timber, and fires in 
the waste destroy young trees. (Photo by U. S. Bureau of Forestry.) 



II. The Adirondacks, with their pine, hemlock, spruce, and hard 
woods. (Figs. 238, 247, and 307.) 

III. The Great Lakes region, especially northern Michigan, Min- 
nesota, and Wisconsin, rich in pine and hemlock. 

IV. The Allegheny Mountains and Plateau, with white pine, 
hemlock, hardwood in the north, and yellow pine and hardwood in 
the south. (Figs. 290, 302, and 308.) 

V. The Gulf region, with yellow pine, cedar, cypress, oak, gum, 

etc. (Fig. 278.) 



• PLANTS, ANIMALS, AND MAN 



477 



VI. The Rocky Mountain region, with bull pine, spruce, and other 
trees. (Fig. 318 and Frontispiece.) 

VII. The Pacific region, the richest of all at present, with its great 
forests of redwood, fir, pine, hemlock, spruce, and cedar. (Figs. 311, 
340, and 343.) 

ANIMAL GEOGRAPHY 

409. Zoological Provinces and Faunas. — In general, animals 
have a greater freedom of movement than plants. The fact 
that they have the power of shifting quickly from place to 




Fig. 345. 



Example of good forestry. Nature will reforest this area, 
by U. S. Bureau of Forestry.) 



(Photo 



place makes them less dependent on their surroundings than 
plants. Most of the forms of animal life can by their power 
of movement escape many dangers, such as frost, fire, and 
floods, that destroy plant life. 



478 ELEMENTS OF PHYSICAL GEOGRAPHY 

A rabbit may nip off the plant, which has no way of escape 
or redress, but when the wolf attempts to eat the rabbit, the 
latter may escape by flight, and the former may move to another 
locality and seek other food. However, there are more or less 
well-defined boundaries beyond which neither the rabbit nor 
the wolf is likely to go. The area over which an aggregate of 
associated animals wander and struggle for existence is called 
a zoological 'province. All the varieties of animals which 
characterize a zoological province constitute its fauna (Fig. 
346). 

The boundaries limiting these provinces are not always 
sharply drawn. There is usually a mingling of the faunas of 
adjoining provinces except where separated by some natural 
feature producing an abrupt change of environment. This 
obstruction to the spread of life is called a barrier. 

The boundaries or barriers that restrain the animals to certain 
provinces or areas are similar in many ways to those which 
control the spread of plants. All barriers are relative and not 
insurmountable. Mountains, deserts, the ocean, changes of 
temperature, the relative abundance of other life in the form 
of food, shelter, or enemies, are all barriers of much importance 
in the study of the distribution of animals as well as plants. 

As with the plants, so with the animals, the ocean forms one 
of the most important of all barriers to land forms, and is the 
chief one in the following broad classification of the surface of 
the earth into zoological regions : 

(1) North American, including North America as far south as the 
Isthmus of Tehuantepec. Its fauna is very similar to that of the 
Eurasian region, and they have more species in common than any of 
the other provinces. Among the forms peculiar to it are the American 
bison, the musk ox, the Rocky Mountain goat. The monkeys, horses, 
and swine do not exist here as indigenous forms. 

(2) Eurasian, including Europe, Africa as far south as the Sahara, 
and Asia north of the Himalayas. Here are large numbers of car- 
nivorous animals, such as the wolf and wild cat, together with the 



480 ELEMENTS OF PHYSICAL GEOGRAPHY 

reindeer, camel, and many varieties of wild sheep and goats. The 
monkey tribe is entirely absent. 

(3) South American, including South America, the West Indies, 
Central America, and southern Mexico. The characteristic forms 
are the tapir, anteater, sloth, llama, and monkey, and the condor 
and rhea among the birds. Equally characteristic is the absence of 
such representative families as oxen, horses, elephants, man-like apes, 
and moles. 

(4) African, including Africa south of the Sahara, southern Arabia, 
and Madagascar. It has the greatest number of species of all the 
provinces, and here the ungulates (hoofed mammals) reach their 
greatest development, over 150 species of this group being known. 
Well-known African animals are the giraffe, hippopotamus, gorilla, 
zebra, ostrich, and lion. The two latter are characteristic, but not 
limited to this province. The most notable absences are the bear 
and deer. 

(5) Oriental, southern Asia and the islands of the East Indies east 
to the Australian region. This province has many types connecting 
it to both the African and Eurasian regions. Species peculiar to it 
are the tiger (also in Eurasian), orang-outang, jungle bear, tapir, and 
several species of antelopes. 

(6) Australian, including Australia, New Zealand (sometimes 
made a sub-province), New Guinea, and other smaller islands. It 
is characterized by the extreme abundance of marsupials, animals 
which carry their young in a pouch, typified by the kangaroo, by the 
very peculiar duckbill, and by the almost complete absence of all 
five higher orders of terrestrial mammals from the apes to the ant- 
eaters. The emu, cassowary, and lyre-bird characterize the bird 
life. 

410. Fresh-water Life. — While some animals are able to 
exist in both fresh and salt water, yet the faunas are so distinct 
as to warrant the separate consideration of fresh-water forms 
(Fig. 347). 

The fresh-water animals, especially those inhabiting the larger 
lakes, are divided into faunas, much as in the ocean. The 
forms of the surface, the shores, and the bottom are usually 
here quite distinct. In the rivers the distinction is less sharply 
marked, while in the ponds and brooks it cannot be drawn. 



PLANTS, ANIMALS, AND MAN 



481 



Fresh-water faunas include amphibians, larval and adult, many 
varieties of fish, the larvae of many types of insects, and some in the 
adult stages, many Crustacea, mollusks, many worms, fresh-water 
sponges, and other lower forms of life. There is great variation 
in these species, for the conditions of fresh-water existence vary 
greatly, from the turbulent brook to the majestic lake. 




Fig. 347. — Salmon at Astoria, Ore. A fish that lives part of the time in 
the ocean and part of the time in fresh water. It runs up the rivers to 
spawn ; the young fish go to the ocean, where they live until ready to spawn. 
(Photo by U. S. Bureau of Fisheries.) 



The transition belt at the mouths of rivers emptying into the ocean, 
where the water is brackish, is hostile to most forms of life, both of 
salt and fresh water, and has a fauna peculiar to itself. 

411. Oceanic Life. — The animal life of the ocean is wonder- 
fully varied and, to the interested observer, full of beauty. As 
exposed on the shores between tides, brought to the surface by 
the dredge and seine, or revealed by the water telescope, the 



482 ELEMENTS OF PHYSICAL GEOGRAPHY 

myriad forms entrance the beholder with their profusion and 
tempt him to further study. 

The distribution of oceanic faunas, while governed by the 
general principles previously outlined, is dependent upon special 
conditions which must be noticed. 

The temperature of the water is the most important factor in the 
distribution of marine animals. It is dependent upon three con- 
ditions, latitude, ocean currents, and depth. 

In general the temperature of the surface oceanic waters is higher 
at the equator and progressively diminishes toward the poles. This 
is, however, modified by the ocean currents, which carry immense 
volumes of warm water into regions where the waters bordering the 
current are considerably colder. The abrupt change thus produced 
is one of the important barriers existing in the ocean. Species may 
be able to extend their range where the change in temperature is 
gradual, but these same species often cannot endure the abrupt change 
of passing from warm to cool water or the contrary. This is espe- 
cially true of the eggs of many of the mollusks. Hence, ocean currents 
often form important boundaries to oceanic provinces. Similarly, 
depth is an important condition, for it directly affects temperature, 
as the farther from the surface the cooler the water. It is closely 
related to the effect of altitude upon the land, a few thousand feet 
vertically causing greater changes in the. faunas than many hundreds 
of miles of latitude. So important is its effect that it is used as the 
basis upon which oceanic life is classified, and the following four great 
life zones are marked off by it. 

Littoral life, that of the shore, is to the ordinary observer 
the best known of any of the oceanic zones. On the beach at 
low tide are found among the seaweed the shore birds, many 
varieties of mollusks with their oddly shaped and often brightly 
colored shells, crabs, sand worms, starfish, sea urchins, in fact, 
representatives of almost every known class of animals. It is 
small wonder that men, from the ancient Greeks to the modern 
scientist, have strongly believed that where land and sea meet, 
life originated. 

The conditions of life here are greatly varied. With the ebb 



PLANTS, ANIMALS, AND MAN 



483 




Fig. 348. — Skate, one of the odd-shaped bottom-living forms of the inter- 
mediate zone. (Photo by U. S, Bureau of Fisheries.) 



484 



ELEMENTS OF PHYSICAL GEOGRAPHY 



and flow of the tide, the dashing of the waves, the winds, the 
sunlight, what more invigorating environment can be con- 
ceived ? 

Intermediate life (sometimes included in littoral) includes 
the life at moderate depths, ranging from low-water level to 
a depth approximating 500 fathoms. It is not sharply separated 
from the littoral and is sometimes included in it. It is the zone 




Fig. 349. 



Jewfish or sea bass, one of the larger fishes of the intermediate 
zone of ocean life. (Photo by E. C. L. Bartow.) 



of seaweeds and corals, and here marine life reaches its maximum 
both in number and variety of forms. Here flourish mollusks 
of many types, including the common clam and oyster, corals, 
sea anemones, sea cucumbers, crinoids or sea lilies, sponges, 
and many lower forms, along with lobsters, crabs, and the vast 
multitude of fishes. Here life conditions, while more uniform 
than those of the littoral zone, have not reached the unvarying 



PLANTS, ANIMALS, AND MAN 485 

monotony of the great deeps. Food is abundant, the depth is 
not too great for sunlight to penetrate, and the waters are 
comparatively warm and undisturbed. (Figs. 348 and 349.) 




Fig. 350. — Deep-sea fishes. They live in perpetual darkness in the cold 
waters at the bottom of the deep sea. (Illustration from Smithsonian Report.) 

Abyssal life. The boundary between the preceding zone and 
the abyssal, or deep sea, is not sharply defined, many species 
passing far to each side of the arbitrary depth taken as the 
dividing line. Conditions of life here are extremely uniform, 
no light, a uniform temperature approximating 34°, great 



486 ELEMENTS OF PHYSICAL GEOGRAPHY 

pressure, little motion of water, and a high percentage of oxy- 
gen. Few plants live here, and the animals are carnivorous, 
feeding upon each other and upon animal remains which slowly 
sink down from the surface. 

Abyssal animals are much the same the world over, and in 
spite of the seeming adverse conditions under which they live, 
the life is quite varied, including all the main types from the 
fishes down. Many of the forms are extremely odd and curious. 
Knowledge of deep-sea life has been greatly extended during 
recent years by the use of the dredge (Figs. 62 and 350). 

Pelagic life includes those forms which habitually live on the sur- 
face of the open sea or at moderate depths below it. Here, under the 
favorable conditions of abundant sunlight and moisture, and with 
many minute forms which furnish food to the larger animals, a rich 
and varied life is found. Whales, many forms of fish, pteropods and 
cephalopods among mollusks, crustaceans, and vast numbers of lower 
forms such as the Portuguese man-of-war, jellyfish, infusoria, fora- 
minifera, and radiolaria, are all pelagic in their habits (Figs. 59 and 61). 

Between the surface zone with its rich fauna and the ocean bottom 
with its scanty fauna is the great body of oceanic waters which, so 
far as our present knowledge shows, is a great watery desert almost 
devoid of life. 

THE GEOGRAPHY OF MAN 

412. Distribution of Mankind. — At one of the World's 
Fairs or on the streets of New York or London, where one can 
see men from all the continents and many of the islands of the 
world, he is impressed with great diversity in color, size, and 
other physical features. Are these people all from one parent 
family, and how came this great diversity in racial character- 
istics ? 

The original habitat of man is thought to be in western Asia, 
from whence descendants migrated in different directions. 
Probably the principal factor in the variations in color, size, 
facial features, and mental development, was geographical 



540,000,000 



PLANTS, ANIMALS, AND MAN 487 

environment. After a long period of time the slow changes 
finally resulted in a great many races and tribes which are 
sometimes grouped in the following five races : 

1. The Ethiopian or black race .... 173,000,000 

2. The Mongolian or yellow race 

3. The Malay or brown race 

4. The American or red race .... 22,170,000 

5. The Caucasian or white race .... 770,000,000 

Total, 1,505,170,000 

The original habitat of the Ethiopian race was in Africa south of 
the Sahara, Madagascar, and many of the East Indies. The second 
and third probably started from the Tibetan table-land. The fourth 
occupied the new world, America. The fifth race probably started 
in North Africa. From the original habitat these races have spread 
over the world and are now mingled on all the continents. 

For many centuries, the red man held undisputed sway in what is 
now the United States. About four centuries ago the white man 
first came in small numbers, then in larger numbers, and later he 
brought the black man, first as a slave. The yellow man found his 
way across the Pacific Ocean and entered our western border. We 
now have all the races in large numbers. So on all the continents 
there is a commingling of different races. 

It must be remembered that the above classification is an arbi- 
trary one, and only one of many attempts to classify the human 
family. Each of the divisions contains many classes and tribes, 
each with its own characteristics of physical and mental traits. There 
are distinctions in size and shape of the skull, color and texture of the 
hair, language, and above all, mental development. A much more 
elaborate classification is given in the Standard Dictionary under " man." 

The Mongolians have probably an older authentic history than 
any of the others, but as far back as their history extends, the Chinese 
and the Japanese branches are separate. They have retained their 
present national characteristics through a longer period of time with 
fewer changes than any of the other nations. 

The peoples who have passed through the greatest changes 
and most rapid development in civilization are some of the 
branches of the Caucasian race. In none of the nations, how- 



488 ELEMENTS OF PHYSICAL GEOGRAPHY 

ever, does authentic history extend back to the beginning of 
the race. That the different races are branches of one common 
family, is an inference or deduction based on a study of the 
whole human family in their physical and mental characteristics, 
and their relations to each other and the other animal forms. 
The origin of the human family is involved in obscurity. 

413. Influence of Geography on Man. — While man by his 
ingenuity has prevailed over the forces of nature in many 
ways, yet it still remains true that he is greatly influenced 
by his geographic surroundings. The climate, topography, 
proximity to the sea, all wield a wonderful influence over 
man. 

414. Climate. — All the great nations of the world have had 
their rise and growth in the temperate climate. This is not a 
coincidence. Man may carry civilization into cold and hot 
climates and may foster it for a time, but the fact remains that 
the development of the great civilized nations has been in the 
temperate zone. 

The continued heat of the tropics tends to make one languid and 
lacking in enterprise. The warm climate requires little clothing or 
shelter to protect one from the elements. The great abundance of 
tropical fruit makes the food supply an easy problem. Thus the 
great incentive to provide food, clothing, and shelter, which arouses 
man to his best efforts in a cooler climate, is lacking in the warm 
tropics. 

In the polar regions the cold is so intense and long continued that 
there is a perpetual struggle for existence ; hence one does not find 
the opportunity to cultivate the mind and surround himself with 
the luxuries and comforts of modern civilization. 

In the temperate region the cold winters rouse man to exertion 
to provide food, clothing, and shelter, and yet the cold is not so 
severe as to dwarf his energies or prevent the development of 
his mental and physical powers. 

415. Influence of Topographic Forms. — As already stated, 
the surface features greatly influence the distribution of the 



PLANTS, ANIMALS, AND MAN 489 

population, as well as the occupations of the people and many 
of their customs and habits. 

The most densely populated areas are generally on the plains, 
because facilities for travel and transportation are there su- 
perior and favor the commercial and manufacturing industries. 
Such conditions also favor agriculture and hence abundant food 
supply. 

Life in the high mountains tends toward the isolation of groups 
of people and the development and perpetuation of local customs. 
There is little communication and intercourse with outside people. 
In the absence of mineral products or large forests the mountain 
people are liable to be poor and live a very simple life with few lux- 
uries. In the primitive and pioneer stages the people in the mountains 
depend largely for support upon hunting and fishing. The charm 
and freedom of such a life compensates in a large measure for the 
absence of any so-called luxuries. When the mountain people are 
dependent on agriculture, the barren soil and rough surface prevent 
any profit more than mere subsistence ; and, hence, the hard struggle 
for food and shelter hinders, if it does not prevent, advancement in 
culture, learning, and conveniences of civilization. 

416. Influence of the Sea. — Proximity to the sea generally 
favors easy communication with other nations and countries, 
and hence fosters the commercial spirit which results in wealth 
and cosmopolitan ideas. In past centuries many of the sea- 
faring nations were warfaring as well and conquered by might, 
while in modern time the battles were fought on manufacturing 
and commercial lines until the great World War began in 1914. 
Let us hope this is the last struggle for military supremacy, and 
that it will mark the downfall of the maxim that " might makes 
right." 

A few examples will best illustrate the influence of geographic 
conditions on man. 

The Eskimo gives all his time and energy to the chase. He has 
no chance to raise vegetables, even if he desires. Having but a 
limited supply of fuel he learns to depend largely on the conservation 



490' ELEMENTS OF PHYSICAL GEOGRAPHY 

of his own bodily heat for warmth, so he dresses in furs, eats fat, and 
lives in ice houses. His life is not devoid of adventure, but there 
is little incentive to advancement, and the Eskimos today are prob- 
ably no better off than their ancestors were centuries ago. 
- The Pygmies of the African forest live in a rude shelter of bushes 
quickly constructed, and hence it is no great hardship to leave it and 
migrate to a distant part of the forest. They have no agriculture, 
and live on nuts and wild animals, which they capture in snares and 
pits. Having no reserve supply of food they are frequently subject 
to hunger and sometimes starvation. There is no development of 
the mental faculties, and they remain but little superior intellectually 
to the animals which they pursue. 

Emigrants from Europe, scarcely four centuries ago, entered 
the present area of the United States. They have cut down 
the forests, cultivated the soil, built cities and factories, ex- 
tended steam railways and electric lines far and wide over the 
land. Many boats ply the inland waters and hundreds of vessels 
sail to and from foreign lands. Telegraph lines extend to dis- 
tant parts of the earth. One may read in the evening papers 
an account of any or all the important events that have hap- 
pened anywhere in the world during the day. If one desires 
he may without leaving his chair talk by telephone with any 
of his friends within a radius of several hundred miles. He 
has in his service many of the varied products of the world ; 
fruits of the field, garden, mine, and factory are at his command. 
What a contrast is this life with that of the Eskimo or the 
African Pygmy ! 

The difference in habits, customs, and civilization and develop- 
ment of these peoples is not entirely due directly to climate, 
but partially to racial differences. The North American 
Indian, who was here before the European, was, and is yet, in 
his natural state, as far below the white in civilization as he is 
superior to the Pygmy. How far these racial differences are 
due to climatic conditions in past ages is a subject worthy of 
consideration. (Fig. 351.) 



PLANTS, ANIMALS, AND MAN 



491 



The influence of geography on the migrations of man, in the found- 
ing of cities, in the construction of highways, has been suggested at 
different places in the preceding chapters and will be constantly sug- 
gested to the student of history and geography in all his study and 
travel. 

The migrations westward from the early settlement at Philadelphia 
first spread out in the Chester — the " Little Valley" — and later in 




Fig. 351. — View in the Spokane Valley, Wash. In its natural state this 
was a semiarid region, almost devoid of vegetation. It is now, through the 
agency of man, a prosperous region, producing a great quantity and variety of 
food crops and supporting a large population. (Photo by Frank Palmer.) 



the "Great Valley," because in these valleys was a rich limestone soil, 
more productive and more easily tilled than that on the bordering 
hills. The further migrations were through the water gaps into the 
other valleys of the Allegheny Mountains, where the people lingered 
long before making the difficult and dangerous journey up and over 
the rocky forested plateau extending west to the Ohio region. Besides 
the great difficulty and danger in traveling, the climate of the plateau 
is more severe and the soil less fertile than in the sheltered valleys 



492 ELEMENTS OF PHYSICAL GEOGRAPHY 

and coves. Hence in the valleys they lingered, until the French were 
pouring into the Ohio Valley by ascending the St. Lawrence and cross- 
ing the Great Lakes and descending the tributaries of the Ohio. 

Pittsburgh was a strategic point in the early colonial days and, 
as Fort Duquesne and Fort Pitt, was the scene of bloody 
conflicts between the nations. The early settlers knew nothing 
of the great coal beds and the deposits of oil and gas that have 
been so instrumental in making this one of the great manu- 
facturing cities of the world, but they could see its advantages 
as a commercial center, and hence, the feverish haste of the 
French to get possession, and of the English to dispossess them. 

It is only necessary to study the geographic location and 
surroundings of New York, Boston, Chicago, Buffalo, and the 
other great cities to see that their growth has been governed 
by ' geographic features, which frequently were not perceived 
by the people at the time, but which governed them, neverthe- 
less. The student from previous reading, study, and observa- 
tion should put in writing the geographic reasons for the location 
and growth of some of our great cities. These should be com- 
pared in the classroom and supplemented by explanations from 
the teacher. 

417. Influence of Man on Geography. — Man is not a mere 
passive agent. While he has been influenced in many ways 
by his geographic surroundings, he has had a very marked 
influence on them in return. As evidence of this one needs 
but to compare the United States of today with its condition 
four centuries ago. 

A large part of the dense forests has been destroyed and the 
area covered with cities, villages, and farms. The freshly 
plowed soil exposed to the rains has been washed in large quan- 
tities into the streams and carried to or toward the sea. In the 
construction of cities, highways, and railways, hills have been 
cut through, sometimes cut down, valleys and lakes have been 
filled or partly filled. Streams have been diverted from their 



PLANTS, ANIMALS, AND MAN 493 

courses. Great dams or lakes have been constructed in some 
places and destroyed in others. Many of the wild animals have 
been wholly or partly destroyed, and domestic animals have 
taken their place. The vast herds of bison that formerly 
roamed over the western plains have disappeared, and their 
place has been taken by cattle, horses, and sheep. Orchards 
have replaced the forest in part', grains, cotton, sugar, and 
vegetables have taken the place of the wild plants over large 
areas. 

Canals have been dug across divides, connecting different 
river basins. The Chicago Drainage Canal carries water from 
Lake Michigan into the Mississippi River, water that under 
natural conditions would drain through the St. Lawrence River. 
Canals connect Lake Erie with the Ohio, and with the Atlantic 
through the Hudson River. The bays, inlets, and lakes along 
the Atlantic Coast have been connected by canals dug by man. 

One of the greatest changes produced by man on the water- 
ways is that of connecting the Atlantic and Pacific Oceans 
through the Panama Canal. In this combat with nature he 
caused an excavation through the dividing mountain range 
of the continent, and conquered the many landslides by means 
of which nature attempted to thwart his purpose. (See Fig. 148.) 

In Chicago, man has not only diverted the waters of Lake Michigan 
across the divide into the Mississippi River, but he has transferred 
vast quantities of rock material from the land into the lake, reclaiming 
a large area from the lake for a city park. 

The people of Seattle have connected beautiful Lake Washington 
with the salt water of the sound, not only enlarging their harbor, but 
giving both fresh water and salt water anchorage. They have also 
dug away many of the hills in the city and dumped them into the 
sound, thus increasing the area along the harbor front and modifying 
the topography of the city. 

The city of Los Angeles has extended its pipe lines 150 miles through 
two mountain ranges and across a desert, to transfer a bountiful 
supply of fresh water into the city. It has also extended a rock wall 
several miles out into the ocean to protect its harbor. 



494 ELEMENTS OF PHYSICAL GEOGRAPHY 

New York City blasted the rocks that impeded navigation out of 
Hell Gate, stretched steel bands over East River, and dug great 
tunnels under the Hudson River. It also constructed the great 
artificial lake, Ashokan, up in the Catskill Mountains, and carries 
the water from this lake under the Hudson River and through many 
miles of pipe line into the city. 

These are only a few of the examples of the geographic changes being 
wrought by man all over the surface of the country. 

The steel bands of the railway connect the oceans at several 
points, and a considerable portion of the intervening territory- 
is covered with a lacework of steel rails over which millions 
of tons of material are being shifted from one part of the country 
to another, and, in connection with the steamboats, part of 
it to distant countries. There .is also the transfer of immense 
quantities of material by electric lines, motor trucks, and 
horse-drawn vehicles. In addition there are many thousands 
of miles of pipe lines, carrying water, oil, and gas. 

Great stone quarries in many places have left holes instead 
of hills. In other places, hills both large and small have been 
built up by the waste from the quarries and mines. Clay, sand, 
gravel, marl, and ore pits are in many places so numerous 
and extensive as to change entirely the surface features of the 
area. 

In many places the mountains and plateaus are bored and 
tunneled by numerous excavations to an extent almost beyond 
belief. Besides the large mine openings man has bored thou- 
sands of deep holes through which have been taken vast ac- 
cumulations of oil and gas. 

Elsewhere, through artesian wells, he has brought the ground- 
water to the surface in arid areas and thus added to the fertility 
of the country. In other localities, where there was too much 
water and the land was swampy, malarial, and unproductive, 
he has by surface or sub-surface draining made it dry, healthful, 
and productive. 

418. Man's Influence on the Geography of Life. — Probably 



PLANTS, ANIMALS, AND MAN 495 

no other factor has had as much influence as man, particularly- 
civilized man, in changing the character of the plant and animal 
life. All through both the animal and plant world there is a 
constant struggle for existence. In this struggle the savage 
differs but little from other animals in any geographic change 
produced. He kills certain animals for food, but in this he 
resembles other carnivorous animals; he uses certain vege- 
tables for food like other herbivorous animals. Civilized 
man, however, has produced widespread and sweeping changes 
in both the plant and animal life. The Indian would kill a 
few trees and plant a few acres of corn here and there, but the 
white man destroys entire forests of thousands of square miles 
and plants the area in wheat, rye, oats, corn, and other food 
crops. He not only cuts down and destroys native plants, but 
he brings others from all parts of the world. In his world- 
wide commerce he not only ships fruits, nuts, and vegetables 
from distant lands, but he transplants the trees and introduces 
a new flora in place of the old. Not only that, but by care in 
cultivation he changes the character of the native plants al- 
most beyond recognition. He has also introduced flowering 
plants, and forest, shade, and ornamental trees and shrubs. 
The stately eucalyptus trees of California have been trans- 
planted from Australia. Most of our orchard trees were 
transplanted from Europe, Asia, or Africa. 

The changes produced in the animal life are nearly as startling. 
There are now millions of horses, cattle, sheep, mules, swine, 
and domestic fowls, where a few centuries ago there were none. 

When the white man first invaded the eastern and central 
states, wild deer, bears, wolves, beavers, and wild turkeys were 
abundant all over the country, now they are to be found only 
in a few limited areas. Probably more than nine-tenths of 
the present population east of the Mississippi River have never 
seen any of these animals except the few kept in captivity. 

A half century ago there were millions of bison roaming in 



496 ELEMENTS OF PHYSICAL GEOGRAPHY 

great herds over the western plains. Now there are none 
except two small herds under government protection in the 
Yellowstone National Park and a few in some of the city parks. 

The graceful antelope that used to be such a common sight 
on the western plains is now a curiosity, outside of the few in 
captivity and a limited number in the Yellowstone Park. 

419. The National Parks. — Owing to the wise provision of 
the government in prohibiting the use of firearms in our na- 
tional parks, these parks, besides their other uses, promise to 
serve as a means of preserving many of the wild animals from 
a speedy extinction. They are proving to be havens of refuge 
for the wild animals that are pursued so relentlessly by the 
hunter. (Fig. 352.) 

There are now (1919) seventeen national parks. Most of 
them have been parks for only a few years, and hence are not 
well stocked with animal life, but in future years they will 
nearly all become homes for the native wild animals. Already, 
one of the attractive features of the Yellowstone, one of 
the oldest national parks, is the abundance and variety of 
native animals that can here be studied in their natural 
surroundings. 

Most of the national parks were made parks for the preserva- 
tion and care of certain geographic or geologic features of 
special interest. They are primarily recreation grounds to 
induce the people to live outdoors and study the wonders of 
nature. 

The Hot Springs Park in Arkansas, the oldest of our national 
parks, was made a park because of the hot springs, and the 
curative properties of the waters have made it primarily a health 
resort. 

The Piatt Park in Oklahoma was made a park because of the 
mineral springs. 

Mt. Rainier in Washington, Crater Lake in Oregon, Lassen 
Peak in California, Mt. McKinley in Alaska, and Hawaiian 



PLANTS, ANIMALS, AND MAN 



497 




498 ELEMENTS OF PHYSICAL GEOGRAPHY 

Park in the Hawaiian Islands are parks for the preservation 
of volcanoes and volcanic phenomena. 

Yellowstone National Park, the second oldest of the parks, 
was made so primarily because of the geysers, but it has many 
other features of interest second only to the geysers, such as 
the hot springs, the petrified forests, the beautiful canyon, the 
waterfalls, lakes, and mountains, comprising beautiful and at- 
tractive scenery. 

Glacier Park, Rocky Mountain Park, Yosemite Park, and 
Sully's Hill Park are parks primarily on account of their scenery. 
Glacier Park in particular contains more attractive scenery 
than any other equal area in the world. The happy com- 
bination of rugged mountains, glaciers, snow fields, waterfalls, 
lakes, forests, and flower-decked areas in Glacier Park is un- 
surpassed anywhere, even in picturesque Switzerland. 

Sequoia and General Grant Parks are for the preservation 
of the giant trees. Wind Cave in South Dakota is a park for 
the preservation of a remarkable cave. Mesa Grande Park in 
Colorado was made to preserve the cliff dwellings. 

Mt. Desert National Park on the coast of Maine is primarily 
for its scenery and secondarily as a refuge for wild animals, 
birds, and flowers. 

Besides the seventeen national parks there are thirty-five 
national monuments, all established since 1906. The dis- 
tinction between the monuments and the parks is that the 
former are created by the President and the latter by Congress. 
In general the parks are larger areas that contain many features, 
and the monuments for the most part are smaller areas with 
often but a single object. 

In a very general classification, four of the national monu- 
ments are caves of special note, six contain objects of historic 
interest, nine are prehistoric, one is a battle field, and fifteen 
contain points of scientific interest or remarkable scenery. 

Both the national parks and the national monuments are 



PLANTS, ANIMALS, AND MAN 499 

places of special interest to the geographer, as he there finds 
the finest examples of geographic features in the midst of most 
attractive surroundings. So impressive are many of the 
features in the parks that they stimulate inquiry and investi- 
gation in the observer. A visit to the glaciers not only invigor- 
ates the body but the mind as well. Most people that see a 
geyser eruption want to know the cause. Who can look into 
the Grand Canyon of the Colorado without being impressed 
with the magnitude of the forces of erosion and with the great 
length of time involved? In addition to the great geographic 
features, the abundance and variety of plant and animal life 
make the national parks and the national monuments places 
of absorbing interest to the intelligent citizens of this country, 
places that will be visited by larger and larger numbers as their 
attractions become better known. 

QUESTIONS 

1. Why is man more independent of his environment than are 
other forms of life ? 

2. Make a list of animals that live only in tropical regions. 

3. Make a list of animals that live only in polar regions. 

4. Make a list of the animals that hibernate during the winter 
months. 

5. Name the plants most commonly found on sandy soil. 

6. Name the plants you have seen growing on hard rocks. 

7. Name the plants that grow in deserts. How does desert 
vegetation differ in general from that in humid regions ? 

8. Why are there no forests on high mountains ? 

9. Why are there no forests at the base of many of the western 
mountains ? 

10. What happens to the shade plants in the forest when the trees 
are cut down ? 

11. What kinds of plants require sunlight? What kinds grow in 
the dark? 

12. Enumerate the ways in which plants are distributed over the 
earth. Can you name any food plants or weeds that are compara- 
tively new in the region where you live ? 



500 ELEMENTS OF PHYSICAL GEOGRAPHY 

13. In some areas where forests have been, cut off, new forests are 
growing, in other areas trees are not growing. Why ? 

14. What effects are produced on farm lands in the valleys by 
destruction of forests on the mountain sides? 

15. Why are there more and larger areas of national forest in the 
western states than in the eastern? 

16. Make a list of the animals that can live in either fresh water 
or salt water. 

17. In what parts of the ocean is life most abundant ? 

18. On what do the animals of the deep ocean bottom feed? 

19. The Indians have inhabited North America many thousand 
years, yet they were never as numerous or as prosperous as the whites 
who have been here less than 500 years. Why? 

20. Why is North America more densely populated than South 
America ? 

21. Make a list of the geographic changes in the United States that 
you have seen, and another of those which you know from reading. 

22. What future geographic changes can you forecast for this 
country? State your reasons. 

23. State the geographic factors that have been instrumental in 
the growth of your native city or the large city nearest to your home. 



APPENDIX I 



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APPENDIX II 



SOME OF THE COMMON METHODS OF MAP PRO- 
JECTION 

The cylindrical projection supposes a cylinder of paper around 
the globe, touching the equator and hence parallel to the axis 
of the globe. On this the meridians and parallels are projected 
at right angles to each other, the meridians forming vertical 
lines and the parallels horizontal ones. The meridians are 
equally spaced and all points on the equator are in their true 

proportion, but toward the 
poles the areas are much 
out of proportion. If the 
projection of the parallels 
is from the center of the 
globe, the pole of the earth 
is at an infinite distance 
and cannot be represented ; 
also the polar regions are 
greatly exaggerated and not 
represented beyond 70 or 75 




Pig. 353. — Cylindrical projection. 



degrees. If the projection of the parallels is at right angles to 
the axis, the polar regions are out of proportion in the opposite 
direction. (See Fig. 353.) 

Mercator's projection is a modified form of the cylindrical, 
in which the parallels are so spaced that the degrees of latitude 
and longitude are in their proper proportions. It is much used 

502 



APPENDIX 



503 







n\j 






<50 \ 


Q 


-^P^V4S° 








/^ 






\---^v"v^\ 


(7$§\. 






^ Globe I 



Fig. 354. — Conical projection. 



by navigators in plotting 

the course at sea, because 

the directions are all true 

and the course can be 

plotted in a straight line. 

(Fig. 14, p. 27, is on Merca- 

tor's projection.) 

In the stereographic pro- 
jection, commonly used in 

mapping the hemispheres, a 

sheet of paper is placed, without curving, parallel to the axis of 

the globe, touching the equator 
at one point in the middle of the 
hemisphere to be mapped. The 
lines are then projected on the 
paper from the point at the 
opposite end of the diameter 
touched by the paper. 

The globular projection differs 
from the stereographic in being 
projected from a point 1.707 
times the radius of the globe. 

The orthographic projection 
differs from the preceding in 
being projected from a point at 
infinity; that is, the lines of 
projection pass through the 
globe parallel to each other and 
normal to the paper. 

The conical projection 

assumes a cone touching the 

earth on the parallel passing 

through the middle of the area 

Fig. 355. — Polar projection. to be mapped, and the lines 




504 ELEMENTS OF PHYSICAL GEOGRAPHY 

projected on the cone from the center of the globe. The cone is 
then split open on a meridian line and spread out flat. This 
is more accurate than any of the preceding for small areas away 
from the equator. In large areas the distortion becomes pro- 
nounced away from the center of the map ; but where greater 
accuracy is .required this defect is sometimes remedied in part 
by using a polyconic projection (Fig. 354). 

In the polar projection, as shown in Fig. 355, the paper is 
placed tangent to the pole, and from the center of the globe 
one point on each parallel is projected to the paper, as at P, Q, 
R. With N (the pole) as a center, circles are drawn through 
these points for the parallels. Radial lines from the center 
(N) form the meridians. 

In none of the above projections is a globe used in actual 
construction, but the lines are located by computation. 



GENERAL REFERENCES 

References for each chapter are given on the following 
pages. Besides these the following books and periodicals 
should be consulted by both teacher and students as oppor- 
tunity offers : 

1. The Face of Nature. Suess. Oxford : University Press. 

2. Geographical Essays. Davis. Boston : Ginn & Co. 

3. The International Geography by 70 Authors. New York: 
D. Appleton & Co. 

4. Forest Physiography of the United States. Bowman. New 
York : John Wiley & Sons. 

5. Textbooks on Geology and Physical Geography. 

6. Publications of the United States Geological Survey. Write to 
the Director, Washington, D. C, for list. 

PERIODICALS 

1. The National Geographic Magazine. Washington, D. C. 

2. The Geographical Review. New York. 

3. Annals of the Association of American Geographers. Washing- 
ton, Conn. 

4. The Journal of Geology. Chicago. 

5. Bulletin of the Geological Society of America. New York. 

6. The Journal of Geography. New York. 

REFERENCES BY CHAPTERS 

CHAPTER I. THE EARTH AS A PLANET 

1. Elements of Descriptive Astronomy. Howe. New York: 
Silver, Burdett & Co. 

2. Manual of Astronomy. Young. Boston: Ginn & Co. 

505 



506 ELEMENTS OF PHYSICAL GEOGRAPHY 

3. Interpretations of Topographic Maps. Salisbury. Professional 
Paper No. 60, U. S. Geological Survey. 

4. Maps and Map Reading. Ravenstein. International Geog- 
raphy. New York : D. Appleton & Co. 

CHAPTER II. THE ATMOSPHERE 

1. Elementary Meteorology. Davis. Boston : Ginn & Co. 

2. Modern Meteorology. Waldo. New York : Charles Scrib- 
ner's Sons. 

3. Popular Treatise on Winds. Ferrel. New York : John 
Wiley & Sons. 

4. Hann's Handbook of Climatology. Ward. New York : The Mac- 
millan Co. 

5. Weather Making, Ancient and Modern. Harrington. Annual 
Report Smithsonian Institution, 1894, pp. 249-271. 

6. Annual Reports, Monthly Weather Review, and Daily Weather 
Map, by the U. S. Weather Bureau. Washington, D. C. 

7. American Weather. Greely. New York : Dodd, Mead & Co. 

8. Meteorological Atlas. Bartholomew. Philadelphia : J. B. 
Lippincott & Co. 

CHAPTER III. THE OCEAN 

1. The Ocean. Murray. New York : Henry Holt & Co. 

2. Physical Geography of the Sea. Maury. New York : D. 
Appleton & Co. 

3. The Depths of the Sea and the Voyage of the Challenger. 
Thompson. New York : The Macmillan Co. 

4. The Gulf Stream. Pillsbury. Annual Report U. S. Coast 
Survey, 1890. 

5. Ocean Currents. Page. Monthly Weather Review, August, 
1902. 

6. Deep Sea Sounding and Dredging. Sigsbee. Washington, 
D. C, 1880. 

7. Deep Sea Exploration. Tanner. U. S. Fish Commission. 
Washington, D. C. 

8. Oceanography of the Pacific. Flint. Bulletin No. 55, U. S. 
National Museum. 

9. Three Cruises of the Blake. Agassiz. Boston : Houghton 
Mifflin Co. 



REFERENCES 507 

10. Strange Fishes of the Deep Sea. Everman. The World 
Today, June and September, 1902. 

11. Marine Hydrographic Survey of the Coasts of the World. 
Littlehales. Eighth International Geological Congress. Washington, 
D. C, 1904. 

12. Reports of the U. S. Fish Commission, and Reports of the 
U. S. Coast and Geodetic Survey. Washington, D. C. 

CHAPTER IV. SHORE LINES AND COAST FEATURES 

1. Shore Processes and Shoreline Development. Johnson. New 
York : John Wiley & Sons. 

2. Beaches and Tidal Marshes. Shaler. National Geographic 
Monographs. New York : American Book Co. 

3. Features of Lake Shores. Gilbert. Fifth Annual Report 
U. S. Geological Survey. 

4. Corals and Coral Islands. Dana. New York : Dodd, Mead & 
Co. 

5. Structure and Distribution of Coral Reefs. Darwin. New 
York : D. Appleton & Co. 

6. Corals and Coral Reefs in the Pacific. Agassiz. Memoir, 
Massachusetts Institute of Comparative Zoology, Harvard Uni- 
versity. 

7. The Geological History of Harbors. Shaler. Thirteenth Annual 
Report U. S. Geological Survey, pp. 93-209. 

CHAPTER V. THE LAND 

1. Manual of Mineralogy and Lithology. Dana. New York: 
John Wiley & Sons. 

2. Washington School Collection of Rocks and Minerals. Howell. 
Washington, D. C. 

3. Collections of Minerals and Rocks. Ward & Co., Rochester, 
N. Y. 

CHAPTER VI. MANTLE ROCK AND SOIL 

1. Origin and Nature of Soils. Shaler. Twelfth Annual Report 
U. S. Geological Survey. 

2. Soils and their Properties. Hilgard. New York: The Mac- 
millan Co. 

3. Rocks, Rock Weathering, and Soils. Merrill. New York : The 
Macmillan Co. 



508 ELEMENTS OF PHYSICAL GEOGRAPHY 

4. Soils. Lyon, Fippin, and Buckman. New York : The Macmil- 
lan Co. 

5. Soil Fertility. Whitney. Farmers' Bulletin No. 257, U. S. 
Department of Agriculture. 

6. Many of the publications of the U. S. Department of Agriculture 
contain valuable information on soils. Write to the Department for 
list. 

CHAPTER VII. GROUNDWATER 

1. Underground Waters of the United States. Fuller. Water 
Supply and Irrigation, Paper No. 114 of the U. S. Geological Survey. 
Many other bulletins of the same series contain excellent articles on 
groundwater. Write to the Director of the U. S. Geological Survey, 
Washington, D. C, for list. 

2. Observations and Experiments on the Fluctuations in Level 
and Rate of Movement of Groundwater. Bulletin No. 5, U. S. 
Weather Bureau. 

3. Chapter on Caves in Aspects of the Earth. Shaler. New 
York : Charles Scribner's Sons. 

4. Artesian Wells. T. C. Chamberlin. Fifth Annual Report U. S. 
Geological Survey, pp. 125-173. 

5. Indiana Caves and their Fauna. W. S. Blatchley. Twenty-first 
Annual Report Indiana Geological Survey, pp. 121-212. 

CHAPTER VIII. RIVERS 

1. Rivers of North America. Russell. New York: G. P. Put- 
nam's Sons. 

2. Rivers and Valleys of Pennsylvania. Davis. National Geo- 
graphic Magazine, Vol. 1, 1889. 

3. Profiles of Rivers. Gannett. U. S. Water-Supply and Irri- 
gation Papers, Bulletin No. 44. 

4. The Flood Plains of Rivers. McGee. Forum, April, 1891. 

5. The Delta of the Rio Colorado. McDougal. Bulletin American 
Geographical Societjr, January, 1906. 

6. The Great Rivers of the World : The Amazon, Mississippi, and 
Yang-tse-Kiang. Journal of Geography, October, November, and 
December, 1910. 

7. North American Natural Bridges. H. F. Cleland. Bulletin Geo- 
logical Society of America, Vol. 21, pp. 313-338. 

8. Base Letel, Grade, and Peneplain. W. M. Davis. Journal of 
Geology, Vol. 10, pp. 77-109. 



REFERENCES 509 

CHAPTER IX. GLACIERS 

1. Glaciers of North America. Russell. Boston : Ginn & Co. 

2. The Great Ice Age. Geikie. New York : D. Appleton & Co. 

3. Glacial Geology. Salisbury. Geological Survey of New Jersey. 
Vol. 5. 

4. Ice Age in North America. Wright. New York : D. Apple- 
ton & Co. 

5. Glacial Lake Agassiz. Upham. Monograph 25, U. S. Geologi- 
cal Survey. 

6. Glacial Lake Iroquois. Fairchild. New York State Museum. 
Twentieth Annual Report State Geologist. Albany, 1900. 

7. Drumlins of New York. Fairchild. Bulletin No. Ill, New 
York State Museum. 

8. The Glacier and Post-Glacial Lakes. Taylor. Smith Report, 
1912. 

9. Characteristics of Existing Glaciers. Hobbs. New York : The 
Macmillan Co. 

CHAPTER X. LAKES AND SWAMPS 

1. Lakes of North America. Russell. Boston: Ginn & Co. 

2. Lake Bonneville. Gilbert. Monograph No. 1, U. S. Geological 
Survey. 

3. Crater Lake. Diller. National Geographic Magazine, Vol. 8, p. 33. 

4. Lakes of Southwest Wisconsin. Fenneman. Wisconsin Geologi- 
cal Survey, Bulletin No. 8. 

5. A Limnological Study of the Finger Lakes of New York. Birge. 
Bulletin Bureau of Fisheries, Vol. 32. 

6. Swamps and Marshes. Shaler. Sixth and Tenth Annual Re- 
ports U. S. Geological Survey. 

7. Classification and Description of Swamps. Harper. Southern 
Woodlands, August, 1908. 

8. Fauna of Oneida Lake. Baker. New York State College of 
Forestry, Syracuse. 

CHAPTER XL CRUSTAL MOVEMENT AND VULCANISM 

1. Textbooks of Geology. 

2. Earthquakes. Hobbs. New York : D. Appleton & Co. 

3. San Francisco Earthquake. National Geographic Magazine, 
May, 1906. 



510 ELEMENTS OF PHYSICAL GEOGRAPHY 

4. Volcanoes of North America. Russell. New York : The Mac- 
millan Co. 

5. Characteristics of Volcanoes. Dana. New York : Dodd, 
Mead & Co. 

CHAPTER XII. PLAINS AND PLATEAUS 

1. High Plains of the United States. Johnson. Twenty-first 
Annual Report U. S- Geological Survey. 

2. The Great Plains of the Centra] United States. Darton. 
Professional Paper No. 33, U. S. Geological Survey. 

3. Coastal Plain of Georgia. Bulletin No. 26, Georgia Geological 
Survey. 

4. Peneplain and Plains of Marine and Subaerial Denudation 
in Geographical Essays. Davis. Boston: Ginn & Co. 

5. Plateau of West Virginia. Campbell and Mendenhall. Seven- 
teenth Annual Report U. S. Geological Survey. 

6. The Enchanted Mesa. Hodge. National Geographic Magazine, 
Vol. 8, 1897. 

7. Canyons of the Colorado. Powell. Meadville, Penna. : Flood 
and Vincent. 

8. The Story of the Prairies. • Willard. Chicago : Rand, McNally 
& Co. 

CHAPTER XIII. MOUNTAINS AND MINOR TOPOGRAPHIC 
FEATURES 

1. Classification of Mountains. Geikie. Scottish Geographical 
Magazine, September, 1901. 

2. Theories of the Origin of Mountain Ranges. Leconte. Journal 
of Geology, Vol. 1. 

3. Northern Appalachians. Willis. National Geographic Mon- 
ographs. New York : American Book Co. 

4. Southern Appalachians. Hayes. National Geographic Mon- 
ographs. New York : American Book Co. 

5. Mechanics of Appalachian Structure. Willis. Thirteenth An- 
nual Report U. S. Geological Survey, Pt. II, p. 217. 

6. Laccolitic Mountain Groups. Cross. Fourteenth Annual 
Report U. S. Geological Survey, Pt. II. 

7. Mountain Ranges of the Great Basin in Geographical Essays. 
Davis. Boston : Ginn & Co. 

8. Origin and Structure of Basin Ranges. Spurr. Bulletin 
American Geological Society, Vol. 12. 



REFERENCES 511 

9. Domes and Dome Structure of the High Sierras. Gilbert. 
Geological Society of America Bulletin, Vol. 15. 

10. Bolson Plains. Keyes. American Geologist, Vol. 34. 

CHAPTER XIV. GEOGRAPHY OF PLANTS, ANIMALS, AND 

MAN 

1. Plant Relations. Coulter. New York: D. Appleton & Co. 

2. Distribution of the Vegetation of Texas. Bray. Bulletin 
No. 82, University of Texas. 

3. Geological Distribution of Animals. Allen. U. S. Geological 
Survey of the Territories, Vol. 4. 

4. The Geographic Distribution of Life in North America. Mer- 
riam. 

5. The Water Hyacinth and its Relation to Navigation. Webber. 
Bulletin No. 18, U. S. Department of Agriculture. 

6. The Physiographic Ecology of Chicago and Vicinity. Cowles. 
Botanical Gazette, Vol. 31, 1901. 

7. Development of the Vegetation of New York State. Bray. 
New York State College of Forestry, Syracuse. 

8. The Earth as Modified by Human Action. Marsh. New York : 
Charles Scribner's Sons. 



INDEX 



Abyssal life, 485 

Adirondack Mountains, 430, 437, 

472, 476 
Aletsch Glacier, 319 
Alkali plains, 224, 406 
Allegheny Mountains, 425, 438, 

443, 476 
Allegheny Plateau, 237, 431, 476 
Alluvial cone, 290 

fan, 289 

plain, 395, 397 

soil, 214 
Alpine glacier, 315 
Aluminum ores, 184 
Anemometer, 66 
Aneroid barometer, 40 
Antecedent river, 306 
Anthracite, 193, 199 ' 

Anticline, 373, 424 
Appalachian Plateau, 409 
Aquifer, 228, 249 
Arid climate, 307, 364 
Arroyo, 308 

Artesian well, 249, 251, 395 
Asteroids, 3 
Atmosphere, 35 
Atoll, 150 
Augite, 177 
Ausable Chasm, 266, 297, 355, 417 

Bacteria, 203 

Bad Lands, 209, 309, 310 

Barogram, 42 

Barograph, 42 

Barometer, 39 

Barriers, 141, 437 

Bars, 139 

Basalt, 198 

Base level, 267 

Bates Hole, 311 

Beach, 136 



Beaumont, Tex., 196 
446, Beaver lakes, 352 

Bergschrund, 317 

Bison, 495 

Black Hills, 250, 429 
-J 30, Blind fish, 231 

Block mountains, 430 

Bolson, 451 

Boothbay, 144-145 

Bore, 109, 129 

Boston Mountains, 443 

Boulder clay, 331, 332 

Boulders, 336, 337 

Breakers, 103 

Breakwater, 162 

Breccia, 191 

Brownsville, Tex., 158 

Buffalo wallow, 451 

Buttes, 448, 449 

Calcite, 185, 244 

Caldera, 386 

Canoe mountains, 426 

Canyons, 412 

Carbonic acid, 212, 230 

Catskill Mountains, 410 

Cave deposits, 241 

Caves, 230 

Chelan Lake, 347 

Chimney rocks, 133, 135 

Chinook wind, 63 

Chittenango Falls, 276 

Cirques, 322 

Clay, 180, 191 

Cliff glaciers, 315 

Climate, 78, 81, 82, 86, 453, 

Cloudburst, 75 

Clouds, 63, 69 

Coal, 193 

Coal Creek, 272 

Coastal plain, 392 

513 



514 



INDEX 



Cold wave, 64 
Colloids, 259 
Colluvial plains, 401 

soils, 223 
Columbia Plateau, 416, 418, 419 
Composition of atmosphere, 36 

of earth's crust, 170 
Concretions, 244, 247 
Conduction, 47 
Conglomerate, 191 
Continental glaciers, 324 

shelf, 95 
Contour maps, 30 
Convection currents, 47 
Copper ores, 183 
Coral, 148 

harbors, 166 

reefs, 148 
Corrasion, 275 
Crater Lake, 350, 386 
Creep, 239, 240 
Crevasse, 293 
Crystals, 173 
Cusp, 139 

Cycle of erosion, 295 
Cyclones, 75 
Cypress, 459 

Day, 22, 23 

Deeps, 96 

Deep sea deposits, 100 

life, 119, 485 

ooze, 100 
Degrees, length of, 15 
Delta harbors, 163 
Deltas, 293, 294 
Deposits, by rivers, 288, 291 

in sea basins, 100 

on continental shelf, 99 
Desert plants, 460 
Dew, 69 
Dew point, 68 
Diatoms, 101, 356 
Dikes, 134, 389 
Diorite, 198 
Dipping needle, 28 
Directions, 10 
Disintegration of rock, 203 
Distributaries, 294 
Doldrums, 54 



Dolomite, 179 
Domed mountains, 428 
Dredges, 97, 98 
Drift, glacial, 332 

oceanic, 115 
Drumlin, 332 
Dry farming, 260 
Dune Park, 154 
Dunes, 154 
Dust, 36 

Earth, a magnet, 26 

composition of, 170 

motions of, 9 

revolution of, 11 

rotation of, 9 

shape of, 6 

size of, 6 

structure of, 8 
Earthquakes, 379 
Earthworms, 214 
Economic features of glaciers, 340 

harbors, 166 

mountains, 439 

ocean, 123 

plains, 397 

plateaus, 416 

swamps, 368 
Eel grass, 147 
Elements, 172 
Environment, 453 
Epiphytes, 457 
Esker, 334 
Eskimo, 489 
Eureka Springs, 254 
Exfoliation, 205 

Falls, 277 
Faults, 376 
Feldspar, 176 
Ferrel's law, 56, 368 
Fiord harbors, 163, 165 
Fish, 124, 481 
Fissures, 376 
Flatirons, 449, 450 
Flood plains, 270 
Fluorite, 188 
Folds, 374 

Forests, 439, 469, 477 
Fossil lakes, 355 



INDEX 



515 



Fossil reefs, 151 

shore lines, 153 
Foucault's pendulum, 9 
Frank landslide, 239 
Frazer River, 273 
Frost, 69 

Gabbro, 198 

Galveston hurricane, 61, 62 

Geographic cycle, 295 

Geysers, 256 

Glacial channels, 335 

lakes, 338, 346-348 

plains, 402 

soils, 221 

striae, 329 
Glaciers, 207, 313-343 

economic effects of, 340 

movements of, 320 

North American, 324 
Glauconite, 102 
Graded streams, 367 
Grand Canyon, 413, 416 
Grand Coulee, 336 
Granite, 197 
Graphite, 187 
Great Lakes, 361 
Great Salt Lake, 154, 356, 402 
Groundwater, 227 
Gulf Stream, 115 
Gypsum, 186 

Hail, 76 
Halite, 185 

Hanging valleys, 323, 326 
Harbors, 160-167 
Hardness, scale of, 173 
Hematite, 180 
Henry Mountains, 428 
Hogback mountains, 449 
Hook, 138 
Hornblende, 177 
Horse latitude, 57 
Hot springs, 256 
Humidity, 67 
Hurricane, 60 
Hygrodeik, 68 
Hygrometer, 68 

Icebergs, 342 
Ice caves, 253 



Igneous rocks, 197 
Induration, 246 
Indus River, 294 
International date line, 23, 27 
Iroquois Lake, 362 
Irrigation, 260, 261 
Islands, 167 
Isobars, 43 
Isoclinal lines, 26 
Isogonic lines, 26 
Isotherms, 51, 53 

John Day River, 400 

Kame, 334 
Kaolin, 180 
Karsten, 236 
Kettle holes, 333 
King's River, 289, 290 
Krakatoa, 214 

Laccolites, 390, 428, 435 
Lacustrine plains, 222, 401 
Lakes, 345-364 

disappearance of, 352, 355 

function of, 358 

in arid regions, 364 

levels, 347, 363 

origin of, 349 
Land, 170 

Landslides, 236, 251 
Latitude, 14, 16-19, 48 
Lava, 385 
Lead ores, 184 
Levee, 291, 292 
Life history of lakes, 359 

of a river, 295 

of mountains, 435 
Life in caves, 231 

in lakes and rivers, 356, 480 
Life zones, 467 
Lightning, 75 
Limestone, 151, 192 
Limonite, 181 
Loess soil, 223 
Lone Pine, Calif., 380 
Longitude, 13, 14, 16, 18, 19 
Los Angeles, 161, 493 
Lost rivers, 234, 308 
Lumbering, 439 



516 



INDEX 



Magnesite, 188 
Magnetism, 26 
Magnetite, 182 
Mammoth Cave, 232 
Man, distribution of, 486 

influence on geography, 492 
Mangrove, 195 
Mantle rock, 203, 215 
Maps, 29, 502 
Marble, 192, 199 
Marengo Cave, 243 
Marl, 368 
Marshes, 365 

Maturity of topography, 296 
Meanders, 270 
Mediterranean seas, 96, 118 
Mercator's projection, 502 
Mesa, 447 

Metamorphic rocks, 198 
Mica, 176 

Mineral springs, 255 
Minerals, 171 
Mining, 443 

Mississippi River, 395, 397-399 
Mississippi Valley earthquake, 380 
Monadnocks, 299, 404 
Monocline, 373 
Monsoon, 64 
Moon, 4 

Moraines, 318, 319, 333 
Mount Pelee, 214, 383 
Mount Pitt, 433 
Mount Rainier, 432 
Mount Vesuvius, 215, 382 
Mountains, 422-446 
Muck, 354 

Nadir, 11 

National forests, 474 

National monuments, 498 

National parks, 496 

Natural Bridge, 236 

Neve, 313 

Niagara Falls, 182, 183 

Nitre, 188, 231 

Nittany Valley, 218 

North Platte River, 414 

Northeaster, 64 

Obsidian, 198 



Ocean, 90-124 

currents, 113 

life in, 118, 421 
Onyx marble, 242 
Oozes, 101 
Ores, 180 

Oswego Harbor, 161, 162 
Ouray, Colo., 267, 435 
Oxbow lakes, 272 
Oxygen, 172, 212 

Palisades, 450 
Panama Canal, 237, 238 
Peat, 193 

Pelagic life, 143, 486 
Peneplain, 298, 404 
Perched boulders, 235 
Periodicals, 505 
Phases of the moon, 4 
Physical geography, xi 
Piedmont glaciers, 315 

plateau, 411 
Pilaster, 242 
Pittsburg, 419, 492 
Plains, 391 
Planetoids, 3 
Planets, 1 

Plant geography, 455 
Plateaus, 409 
Playas, 309, 365, 451 
Plow sole, 218 
Polar projection, 504 
Porpoise, 119 
Potholes, 283, 330 
Potomac River, 286 
Powder River, 194 
Prairies, 408, 465 
Precipitation, 72 
Pressure of the air, 38, 50 
Projections, 502 
Public lands, 19 
Pumice, 198 
Pygmy, 490 
Pyrite, 183 

Quaking bogs, 366 
Quartz, 175 
Quartzite, 199 

Rainfall, 72, 83, 84 



INDEX 



517 



Rapids, 277 
References, 505 
Residual soil, 220 
Reversed drainage, 293 
Revived rivers, 300 
Revolution of the earth, 11 
River deposits, 288 

piracy, 302 

profile, 268 
Rivers, 263-311 
Rocking stones, 335 
Rocks, 189 
Rust, 203 

Salt, 185 
Salt lakes, 365 

marshes, 368 

plains, 406 
Salton sink, 350, 397 
Salts of the ocean, 93 
San Francisco earthquake, 378, 379 
Sand dunes, 154 
Sandstone, 191 
Sargasso seas, 114 
Sargassum, 113 
Sea caves, 134 

density of, 118 

depth of, 96 

temperature of, 98, 116 

water, composition of, 93 
Seaports, 160 
Seasons, 11 
Seattle, 493 
Sedimentary rocks, 191 
Seepage, 255 
Shale, 191 

Shenandoah River, 305 
Shore cliff, 131 

lines, 126-168 

terraces, 153, 372 
Shoshone River, 301 
Silver Spring, 253 
Sink holes, 233, 234 
Sleet, 72 
Snow fields, 313 
Soil, 203, 218-226, 259, 455 
Solar day, 22 

system, 1, 3, 501 

time, 23 
Sounding, 97 



Spit, 138 

Spouting caves, 138 
Springs, 242, 252, 254 
Squid, 120 
Stalactite, 241 
Stalagmite, 242 
Standard time, 24 
Stocks, 390 

Subsequent streams, 305 
Sulphur, 186 
Sun, 5 

Superimposed rivers, 306 
Swamps, 365 
Syenite, 198 
Syncline, 373 

Talc, 188 
Talus cones, 290 
Temperature, 44, 45, 51 
Terraced mountains, 425 
Terraces, 300, 372 
Thermogram, 45 
Thermograph, 46 
Thermometer, 45 
Thunderstorm, 74 
Tides, 106-110 
Timber line, 442, 463 
Time, 22 

Topographic Atlas, 32 
Topography, 'influence of, 51 

of ocean bottom, 94 

of shore lines, 132 
Tornado, 62 
Trade wind, 56 

Transportation by rivers, 284, 286 
Travertine, 244, 245 
Trick Falls, 235, 282 
Tripoli, 356 
Tufa, 192, 198, 244 
Tundras, 407 

Uncompaghre Creek, 367 
Undertow, 103, 113, 130 
Universe, 3 

Vegetation, 455 

Veins, 240 

Volcanic harbor, 165, 166 

materials, 384 

mountains, 434 



518 



INDEX 



Volcano, 381 

Wadies, 308 

Water, effect on life, 457 

gaps, 302, 303 

plants, 458 

table, 228, 229 

vapor, 37 
Waterfalls, 277 
Waterspout, 63 
Watkins Glen, 33, 280 
Waves, 102-6, 129, 130 
Weather, 75 

forecast, 76, 78 

maps, 77, 79 
Weathering, 203, 205 



Wells, artesian, 249 

common, 248 
Whistling caves, 136 
Wind, 54-66, 85 

gaps, 303 
Work of rivers, 274 
Wyandotte Cave, 230 

Yellowstone Falls, 281, 282 
Youth of a river, 296 

Zenith, 11 
Zinc ores, 184 
Zones, 52, 81, 457 
Zoological provinces, 477 



